CSAT (Paper II): previous-year questions
1280 real UPSC Prelims questions (2011–2026) with the official answer and a clear explanation. 400 of them came in the last five papers.
How often UPSC asks this
Questions per year, counted from the official papers.
Subtopics
Arrangements, ranking, ordering and puzzles
142 questions
Clocks and calendars
5 questions
Coding-decoding, series, patterns, cubes, dice and visual reasoning
110 questions
Communication, interpersonal skills and decision-making
10 questions
Counting, permutations, combinations and probability
1 questions
Directions, blood relations and Venn diagrams
60 questions
General English: grammar, vocabulary and comprehension
20 questions
General Hindi: grammar, vocabulary, dialects and comprehension
25 questions
Geometry and mensuration
26 questions
Number system and basic algebra (divisibility, HCF/LCM, remainders, digits, equations)
196 questions
Percentages, profit and loss, discount, simple and compound interest
47 questions
Ratio, proportion, averages, mixtures and alligation
47 questions
Syllogisms, statements and conclusions, assumptions and arguments
89 questions
Time and work; pipes and cisterns
2 questions
Time, speed and distance; trains, boats and streams; races
48 questions
Attempt the questions
Newest papers first. Tap an option; the answer and the reason appear instantly.
There were 50 faculty members comprising 30 males and the rest females. No male faculty member knew music, but many of the female faculty members did. The Head of the institution invited six faculty members to a tea party by draw of lots. At the party it was discovered that no member knew music. The conclusion is that :
Answer (d) & explanation
Nothing can be said about the gender mix of the party (d). Step 1: no male knew music. But only "many", not all, of the 20 women knew music. So some women may not know music. Step 2: the six chosen people knew no music. They could be all men, all women who do not know music, or a mix of both. Step 3: so option (a), only men, is not certain. Option (b), only non-musical women, is not certain. Option (c), both men and women, is also only possible. None of them must be true.
Tip: "many" and "some" never mean "all". When a group is chosen by lottery, any combination that fits the facts is possible, so be slow to draw a conclusion.
Answer as per the official UPSC answer key.
Read the passage
Understanding of the role of biodiversity in the hydrological cycle enables better policy-making. The term biodiversity refers to the variety of plants, animals, microorganisms, and the ecosystems in which they occur. Water and biodiversity are interdependent. In reality, the hydrological cycle decides how biodiversity functions. In turn, vegetation and soil drive the movement of water. Every glass of water we drink has, at least in part, passed through fish, trees, bacteria, soil and other organisms. Passing through these ecosystems, it is cleansed and made fit for consumption. The supply of water is a critical service that the environment provides.
Which among the following is the most critical inference that can be made from the above passage ?
Answer (a) & explanation
The best inference is that biodiversity keeps nature's water cycle going (a). Step 1: the passage says vegetation and soil "drive the movement of water", and ecosystems cleanse it. So living things sustain nature's water recycling. Step 2: option (b) says we cannot get drinking water without living things. The passage says water passes through organisms "at least in part", so "cannot" overstates it. Step 3: option (c), about organisms interacting, is true but beside the point. Option (d) is about how life began, which the passage does not discuss.
Tip: pick the option that sums up the passage's link. Options that go further than the passage, like "cannot", are traps.
Answer as per the official UPSC answer key.
A and B walk around a circular park. They start at 8 a.m. from the same point in the opposite directions. A and B walk at a speed of 2 rounds per hour and 3 rounds per hour respectively. How many times shall they cross each other after 8.00 a.m. and before 9.30 a.m.?
Answer (a) & explanation
They cross each other 7 times (a). Step 1: they walk in opposite directions, so their speeds add: 2 + 3 = 5 rounds per hour. Together they cover one full round every 60 ÷ 5 = 12 minutes. So they meet every 12 minutes. Step 2: from 8:00 to 9:30 is 90 minutes. They meet at 8:12, 8:24, 8:36, 8:48, 9:00, 9:12 and 9:24. Step 3: the next meeting is at 9:36, which is too late. So they cross 7 times. Option (b), 6, misses one. Option (c), 5, uses 1 hour. Option (d), 8, counts 9:36.
Tip: in circular tracks, opposite directions add speeds and the same direction subtracts them.
Answer as per the official UPSC answer key.
Read the passage
Biomass as fuel for power, heat, and transport has the highest mitigation potential of all renewable sources. It comes from agriculture and forest residues as well as from energy crops. The biggest challenge in using biomass residues is a long-term reliable supply delivered to the power plant at reasonable costs; the key problems are logistical constraints and the costs of fuel collection. Energy crops, if not managed properly, compete with food production and may have undesirable impacts on food prices. Biomass production is also sensitive to the physical impacts of a changing climate.
Projections of the future role of biomass are probably overestimated, given the limits to the sustainable biomass supply, unless breakthrough technologies substantially increase productivity. Climate-energy models project that biomass use could increase nearly four-fold to around 150 — 200 exajoules, almost a quarter of world primary energy in 2050. However the maximum sustainable technical potential of biomass resources (both residues and energy crops) without disruption of food and forest resources ranges from 80 — 170 exajoules a year by 2050, and only part of this is realistically and economically feasible. In addition, some climate models rely on biomass-based carbon capture and storage, an unproven technology, to achieve negative emissions and to buy some time during the first half of the century.
Some liquid biofuels such as corn-based ethanol, mainly for transport, may aggravate rather than ameliorate carbon emissions on a life-cycle basis. Second generation biofuels, based on ligno-cellulosic feedstocks — such as straw, bagasse, grass and wood — hold the promise of sustainable production that is high-yielding and emit low levels of greenhouse gases, but these are still in the R & D stage.
Which of the following can lead to food security problem ?
- 1. Using agricultural and forest residues as feedstock for power generation
- 2. Using biomass for carbon capture and storage
- 3. Promoting the cultivation of energy crops
Select the correct answer using the code given below :
Answer (b) & explanation
Only promoting energy crops threatens food security (b). Step 1: the passage says energy crops "compete with food production and may have undesirable impacts on food prices". So statement 3 is a food security risk. Step 2: agricultural and forest residues (statement 1) are left over after the harvest. Using them takes no food away. Step 3: carbon capture and storage with biomass (statement 2) is described as an unproven technology. It is a climate issue, not a food issue. So options (a), (c) and (d) fail.
Tip: link each statement to the exact problem the passage pins on it. Residues and waste are usually shown as the "safe" choice in biomass passages.
Answer as per the official UPSC answer key.
When three friends A, B and C met, it was found that each of them wore an outer garment of a different colour. In random order, the garments are: jacket, sweater and tie; and the colours are: blue, white and black. Their surnames in random order are: Ribeiro, Kumar and Singh. Further, we know that :
- 1. neither B nor Ribeiro wore a white sweater
- 2. C wore a tie
- 3. Singh's garment was not white
- 4. Kumar does not wear a jacket
- 5. Ribeiro does not like to wear the black colour
- 6. Each of the friends wore only one outer garment of only one colour
What is C's surname ?
Answer (a) & explanation
C's surname is Ribeiro (a). Step 1: someone wore the white sweater. It was not B (clue 1) and not C, who wore the tie (clue 2). So A wore the white sweater. Step 2: A is not Ribeiro (clue 1) and not Singh, whose garment was not white (clue 3). So A is Kumar. Step 3: clue 1 names B and Ribeiro as two different people. So B is not Ribeiro, which makes C Ribeiro and B Singh. Options (b) Kumar and (c) Singh belong to A and B. Option (d) fails because the clues settle it.
Tip: clues like "neither B nor Ribeiro" quietly tell you B and Ribeiro are different people. Use such hidden facts.
Answer as per the official UPSC answer key.
Read the passage
Accountability, or the lack of it, in governance generally, and civil services, in particular, is a major factor underlying the deficiencies in governance and public administration. Designing an effective framework for accountability has been a key element of the reform agenda. A fundamental issue is whether civil services should be accountable to the political executive of the day or to society at large. In other words, how should internal and external accountability be reconciled ? Internal accountability is sought to be achieved by internal performance monitoring, official supervision by bodies like the Central Vigilance Commission and Comptroller and Auditor General, and judicial review of executive decisions. Articles 311 and 312 of the Indian Constitution provide job security and safeguards to the civil services, especially the All India Services. The framers of the Constitution had envisaged that provision of these safeguards would result in a civil service that is not totally subservient to the political executive but will have the strength to function in larger public interest. The need to balance internal and external accountability is thus built into the Constitution. The issue is where to draw the line. Over the years, the emphasis seems to have tilted in favour of greater internal accountability of the civil services to the political leaders of the day who in turn are expected to be externally accountable to the society at large through the election process. This system for seeking accountability to society has not worked out, and has led to several adverse consequences for governance.
Some special measures can be considered for improving accountability in civil services. Provisions of articles 311 and 312 should be reviewed and laws and regulations framed to ensure external accountability of civil services. The proposed Civil Services Bill seeks to address some of these requirements. The respective roles of professional civil services and the political executive should be defined so that professional managerial functions and management of civil services are depoliticized. For this purpose, effective statutory civil service boards should be created at the centre and in the states. Decentralization and devolution of authority to bring government and decision making closer to the people also helps to enhance accountability.
According to the passage, which of the following factor/factors led to the adverse consequences for governance/public administration ?
- 1. Inability of civil services to strike a balance between internal and external accountabilities
- 2. Lack of sufficient professional training to the officers of All India Services
- 3. Lack of proper service benefits in civil services
- 4. Lack of Constitutional provisions to define the respective roles of professional civil services vis-a-vis political executive in this context
Select the correct answer using the code given below :
Answer (c) & explanation
The answer is 1 and 4 only (c). Step 1: the passage says the tilt towards internal accountability to political leaders "has led to several adverse consequences". That is the failure to balance internal and external accountability, so statement 1 is right. Step 2: it also says the roles of civil servants and the political executive should be defined, which means they are not clearly defined now. So statement 4 is right. Step 3: training of officers (2) and service benefits (3) are never mentioned. So options (a), (b) and (d) fail.
Tip: in "according to the passage" questions, tick a statement only if you can point to a line that supports it. Sensible ideas from outside the passage do not count.
Answer as per the official UPSC answer key.
The monthly average salary paid to all the employees of a company was Rs. 5000. The monthly average salary paid to male and female employees was Rs. 5200 and Rs. 4200 respectively. Then the percentage of males employed in the company is :
Answer (b) & explanation
Males are 80% of the staff (b). Step 1: use alligation. The overall average is Rs 5000. Males earn Rs 5200, which is 200 above it. Females earn Rs 4200, which is 800 below it. Step 2: the counts are in the reverse ratio of these gaps. Males : females = 800 : 200 = 4 : 1. Step 3: males = 4 out of 5 = 80%. Option (a), 75%, would give an average of 4950. Options (c) and (d) give averages above 5000.
Tip: in mixture averages, the bigger group sits closer to the overall average. Since 5000 is much closer to 5200, males must be the large majority.
Answer as per the official UPSC answer key.
Read the passage
All humans digest mother’s milk as infants, but until cattle began being domesticated 10,000 years ago, children once weaned no longer needed to digest milk. As a result, they stopped making the enzyme lactase, which breaks down the sugar lactose into simple sugars. After humans began herding cattle, it became tremendously advantageous to digest milk, and lactose tolerance evolved independently among cattle herders in Europe, the middle East and Africa. Groups not dependant on cattle, such as the Chinese and Thai, remain lactose intolerant.
Which among the following is the most logical assumption that can be made from the above passage ?
Answer (b) & explanation
The logical assumption is that a lasting change in food habits can bring a genetic change (b). Step 1: the passage says herding made milk a lasting food, and lactose tolerance evolved among herders. So a long-term diet change led to a genetic change. That is option (b). Step 2: option (a), about domestication 10,000 years ago, restates a fact rather than an assumption. Step 3: option (c) says only lactose-tolerant people get simple sugars, and option (d) says intolerant people cannot digest any dairy. Both overgeneralise; many people digest curd and cheese.
Tip: an assumption is the hidden link the author needs. Facts already stated in the passage are not assumptions.
Answer as per the official UPSC answer key.
Five people A, B, C, D and E are seated about a round table. Every chair is spaced equidistant from adjacent chairs.
- (i) C is seated next to A
- (ii) A is seated two seats from D
- (iii) B is not seated next to A
On the basis of above information, which of the following must be true ?
- 1. D is seated next to B
- 2. E is seated next to A
- 3. D and C are separated by two seats
Select the correct answer using the code given below :
Answer (b) & explanation
Statements 1 and 2 must be true (b). Step 1: with five seats, A has two neighbours. B cannot sit next to A, and D sits two seats away, so not next to A either. So A's neighbours are C and E. Statement 2 is true. Step 2: the two seats that are not next to A are next to each other. B and D take them. So D sits next to B, and statement 1 is true. Step 3: the order could be A, C, D, B, E or A, C, B, D, E. In the second case D and C are not two seats apart. So statement 3 need not be true.
Tip: in seating puzzles, place the person with the most rules first. Then try every arrangement left before saying something "must" be true.
Answer as per the official UPSC answer key.
Read the passage
In the last decade, the banking sector has been restructured with a high degree of automation and products that mainly serve middle-class and upper middle-class society. Today there is a need for a new agenda for the banking and non-banking financial services that does not exclude the common man.
Which one of the following is the message that is essentially implied in the above passage ?
Answer (d) & explanation
The implied message is the need to promote financial inclusion (d). Step 1: the passage says banking mainly serves the middle classes, and a new agenda must not "exclude the common man". That is financial inclusion. Step 2: option (a), more automation, is part of the problem the passage describes, not the cure. Step 3: option (b), restructuring the whole public finance system, goes beyond banking. Option (c), integrating banks and non-banks, is not raised.
Tip: financial inclusion means bringing the poor and rural people into banking: accounts, credit and insurance. Schemes like Jan Dhan accounts are real-life examples.
Answer as per the official UPSC answer key.
W can do 25% of a work in 30 days, X can do 1/4 of the work in 10 days, Y can do 40% of the work in 40 days and Z can do 1/3 of the work in 13 days. Who will complete the work first?
Answer (d) & explanation
Z will finish first (d). Step 1: work out each person's time for the whole job. W does 25% in 30 days, so the whole job takes 4 × 30 = 120 days. X does 1/4 in 10 days, so 40 days. Step 2: Y does 40% in 40 days, so 40 ÷ 0.4 = 100 days. Z does 1/3 in 13 days, so 3 × 13 = 39 days. Step 3: the shortest time is Z's 39 days. Option (b), X, is close at 40 days but slower. Options (a) W and (c) Y are much slower.
Tip: put everyone on the same base, the full job, before comparing. Close numbers like 39 and 40 are the setter's trap.
X looks fastest at a glance. Z's 1/3 in 13 days is just quicker.
Answer as per the official UPSC answer key.
Read the passage
Biomass as fuel for power, heat, and transport has the highest mitigation potential of all renewable sources. It comes from agriculture and forest residues as well as from energy crops. The biggest challenge in using biomass residues is a long-term reliable supply delivered to the power plant at reasonable costs; the key problems are logistical constraints and the costs of fuel collection. Energy crops, if not managed properly, compete with food production and may have undesirable impacts on food prices. Biomass production is also sensitive to the physical impacts of a changing climate.
Projections of the future role of biomass are probably overestimated, given the limits to the sustainable biomass supply, unless breakthrough technologies substantially increase productivity. Climate-energy models project that biomass use could increase nearly four-fold to around 150 — 200 exajoules, almost a quarter of world primary energy in 2050. However the maximum sustainable technical potential of biomass resources (both residues and energy crops) without disruption of food and forest resources ranges from 80 — 170 exajoules a year by 2050, and only part of this is realistically and economically feasible. In addition, some climate models rely on biomass-based carbon capture and storage, an unproven technology, to achieve negative emissions and to buy some time during the first half of the century.
Some liquid biofuels such as corn-based ethanol, mainly for transport, may aggravate rather than ameliorate carbon emissions on a life-cycle basis. Second generation biofuels, based on ligno-cellulosic feedstocks — such as straw, bagasse, grass and wood — hold the promise of sustainable production that is high-yielding and emit low levels of greenhouse gases, but these are still in the R & D stage.
In the context of using biomass, which of the following is/are the characteristic/characteristics of the sustainable production of biofuel ?
- 1. Biomass as a fuel for power generation could meet all the primary energy requirements of the world by 2050
- 2. Biomass as a fuel for power generation does not necessarily disrupt food and forest resources
- 3. Biomass as a fuel for power generation could help in achieving negative emissions, given certain nascent technologies
Select the correct answer using the code given below :
Answer (c) & explanation
Statements 2 and 3 are right (c). Step 1: the passage says 80 to 170 exajoules a year could come from biomass "without disruption of food and forest resources". So statement 2 holds. Step 2: biomass with carbon capture can give "negative emissions", using nascent technologies. So statement 3 holds. Step 3: statement 1 says biomass could meet all the world's primary energy needs by 2050. The passage gives it about a quarter. So statement 1 is wrong, and options (a), (b) and (d) fail.
Tip: numbers are a common trap. When a statement says "all" and the passage gives a fraction, reject it.
Answer as per the official UPSC answer key.
(Same information as the question above.)
What is the colour of the tie ?
Answer (b) & explanation
The tie is blue (b). Step 1: C wears the tie, and C is Ribeiro. Step 2: white is already A's colour, because A wore the white sweater. Step 3: Ribeiro does not wear black (clue 5). So the only colour left for the tie is blue. B, Singh, then wears the black jacket. Option (a), black, is ruled out by clue 5. Option (c), white, belongs to A. Option (d) fails because the colour is fixed.
Tip: once names and garments are fixed, colours fall into place quickly. Build a small table with rows for A, B and C and columns for surname, garment and colour. Fill it in as each clue settles a box.
Answer as per the official UPSC answer key.
Read the passage
Accountability, or the lack of it, in governance generally, and civil services, in particular, is a major factor underlying the deficiencies in governance and public administration. Designing an effective framework for accountability has been a key element of the reform agenda. A fundamental issue is whether civil services should be accountable to the political executive of the day or to society at large. In other words, how should internal and external accountability be reconciled ? Internal accountability is sought to be achieved by internal performance monitoring, official supervision by bodies like the Central Vigilance Commission and Comptroller and Auditor General, and judicial review of executive decisions. Articles 311 and 312 of the Indian Constitution provide job security and safeguards to the civil services, especially the All India Services. The framers of the Constitution had envisaged that provision of these safeguards would result in a civil service that is not totally subservient to the political executive but will have the strength to function in larger public interest. The need to balance internal and external accountability is thus built into the Constitution. The issue is where to draw the line. Over the years, the emphasis seems to have tilted in favour of greater internal accountability of the civil services to the political leaders of the day who in turn are expected to be externally accountable to the society at large through the election process. This system for seeking accountability to society has not worked out, and has led to several adverse consequences for governance.
Some special measures can be considered for improving accountability in civil services. Provisions of articles 311 and 312 should be reviewed and laws and regulations framed to ensure external accountability of civil services. The proposed Civil Services Bill seeks to address some of these requirements. The respective roles of professional civil services and the political executive should be defined so that professional managerial functions and management of civil services are depoliticized. For this purpose, effective statutory civil service boards should be created at the centre and in the states. Decentralization and devolution of authority to bring government and decision making closer to the people also helps to enhance accountability.
With reference to the passage, the following assumptions have been made :
- 1. Political executive is an obstacle to the accountability of the civil services to the society
- 2. In the present framework of Indian polity, the political executive is no longer accountable to the society
Which of these assumptions is/are valid ?
Answer (a) & explanation
Only assumption 1 is valid (a). Step 1: the passage says routing accountability through political leaders "has not worked out", and calls for depoliticising the civil services. So the author treats the political executive as a block between civil servants and society. Assumption 1 holds. Step 2: the passage also says politicians are accountable to society "through the election process". So assumption 2, that they are no longer accountable, goes against the passage. Step 3: so options (b), (c) and (d) fail.
Tip: an assumption must fit what the author already believes. If the passage says the opposite of a statement, as here with elections, reject that statement at once.
Answer as per the official UPSC answer key.
Six boxes A, B, C, D, E and F have been painted with six different colours viz., violet, indigo, blue, green, yellow and orange and arranged from left to right (not necessarily either kept or painted with the colours in the same order). Each box contains a ball of any one of the following six games: cricket, hockey, tennis, golf, football and volleyball (not necessarily in the same order). The golf ball is in violet box and is not in the box D. The box A which contains tennis ball is orange in colour and is at the extreme right. The hockey ball is neither in box D nor in box E. The box C having cricket ball is painted green. The hockey ball is neither in the box painted blue nor in the box painted yellow. The box C is fifth from right and next to box B. The box B contains volleyball. The box containing the hockey ball is between the boxes containing golf ball and volleyball.
Which one of the following boxes contains the golf ball ?
Answer (b) & explanation
The golf ball is in box E (b). Step 1: box A has tennis and is orange, at the far right. Box C has cricket and is green, fifth from the right. Box B, next to C, has volleyball. Step 2: that leaves golf, hockey and football for D, E and F. Golf is not in D. Hockey is in neither D nor E, so hockey is in F. Step 3: golf cannot go in D, so golf is in E, and football is in D. The violet box is E. Option (a) F has hockey. Option (c) D has football. Option (d) fails because E works.
Tip: in box puzzles, place the fixed facts first. Then use "not" clues to fill the last few gaps.
Answer as per the official UPSC answer key.
Read the passage
“The conceptual difficulties in National Income comparisons between underdeveloped and industrialised countries are particularly serious because a part of the national output in various underdeveloped countries is produced without passing through the commercial channels.”
In the above statement, the author implies that :
Answer (b) & explanation
The author implies that a non-commercial sector makes income comparisons between countries difficult (b). Step 1: the passage says comparisons are hard "because a part of the national output… is produced without passing through the commercial channels". In poor countries, people grow and consume much of their own output. Step 2: so option (b) captures the point. Step 3: option (a) says the entire output in rich countries passes through markets, which is too extreme. Option (c) tells us what should happen, a prescription the author never makes. Option (d) calls it a sign of underdevelopment, which is not claimed.
Tip: GDP counts mostly market transactions, so unpaid home work and own-farm food are often missed.
Answer as per the official UPSC answer key.
There are five hobby clubs in a college — photography, yachting, chess, electronics and gardening. The gardening group meets every second day, the electronics group meets every third day, the chess group meets every fourth day, the yachting group meets every fifth day and the photography group meets every sixth day. How many times do all the five groups meet on the same day within 180 days?
Answer (d) & explanation
All five groups meet together 3 times (d). Step 1: the groups meet every 2, 3, 4, 5 and 6 days. They all meet on the same day only on days that are multiples of every one of these numbers. Step 2: find the LCM of 2, 3, 4, 5 and 6. 4 = 2 × 2 and 6 = 2 × 3, so LCM = 2 × 2 × 3 × 5 = 60. They all meet every 60 days. Step 3: within 180 days that is days 60, 120 and 180, so 180 ÷ 60 = 3 times. Option (b), 18, comes from dividing by 10 by mistake. Options (a) and (c) do not fit.
Tip: "when do things happen together again" is almost always an LCM question.
2 × 3 × 4 × 5 × 6 = 720 is not the LCM. Use the LCM.
Answer as per the official UPSC answer key.
Read the passage
Safe and sustainable sanitation in slums has immeasurable benefits to women and girls in terms of their health, safety, privacy and dignity. However, women do not feature in most of the schemes and policies on urban sanitation. The fact that even now the manual scavenging exists, only goes to show that not enough has been done to promote pour-flush toilets and discontinue the use of dry latrines. A more sustained and rigorous campaign needs to be launched towards the right to sanitation on a very large scale. This should primarily focus on the abolition of manual scavenging.
With reference to the above passage, consider the following statements :
- 1. Urban sanitation problems can be fully solved by the abolition of manual scavenging only
- 2. There is a need to promote greater awareness on safe sanitation practices in urban areas
Which of the statements given above is/are correct?
Answer (b) & explanation
Only statement 2 is correct (b). Step 1: the passage calls for a "sustained and rigorous campaign" on sanitation. So more awareness about safe sanitation is needed, and statement 2 holds. Step 2: statement 1 says sanitation problems can be "fully solved" by abolishing manual scavenging "only". The passage makes abolition the main focus, but never says it alone fixes everything. Step 3: so statement 1 goes too far, and options (a), (c) and (d) fail.
Tip: strong words like "fully" and "only" turn a reasonable idea into a false statement. Manual scavenging is banned by a 2013 Act, but sanitation needs much more than one ban.
Answer as per the official UPSC answer key.
The average monthly income of a person in a certain family of 5 is Rs. 10,000. What will be the average monthly income of a person in the same family if the income of one person increased by Rs. 1,20,000 per year?
Answer (a) & explanation
The new average is Rs 12,000 (a). Step 1: the family's total monthly income = 5 × 10,000 = Rs 50,000. Step 2: one person's income rises by Rs 1,20,000 a year. That is 1,20,000 ÷ 12 = Rs 10,000 a month. Step 3: new total = 50,000 + 10,000 = 60,000. New average = 60,000 ÷ 5 = Rs 12,000. Option (d), Rs 34,000, wrongly adds the yearly figure to the monthly one. Options (b) and (c) do not fit.
Tip: watch the time units. Convert yearly to monthly (divide by 12) before mixing figures. An increase shared over 5 people raises the average by one-fifth of it.
Rs. 34,000 adds the yearly figure to a monthly average.
Answer as per the official UPSC answer key.
Read the passage
Biomass as fuel for power, heat, and transport has the highest mitigation potential of all renewable sources. It comes from agriculture and forest residues as well as from energy crops. The biggest challenge in using biomass residues is a long-term reliable supply delivered to the power plant at reasonable costs; the key problems are logistical constraints and the costs of fuel collection. Energy crops, if not managed properly, compete with food production and may have undesirable impacts on food prices. Biomass production is also sensitive to the physical impacts of a changing climate.
Projections of the future role of biomass are probably overestimated, given the limits to the sustainable biomass supply, unless breakthrough technologies substantially increase productivity. Climate-energy models project that biomass use could increase nearly four-fold to around 150 — 200 exajoules, almost a quarter of world primary energy in 2050. However the maximum sustainable technical potential of biomass resources (both residues and energy crops) without disruption of food and forest resources ranges from 80 — 170 exajoules a year by 2050, and only part of this is realistically and economically feasible. In addition, some climate models rely on biomass-based carbon capture and storage, an unproven technology, to achieve negative emissions and to buy some time during the first half of the century.
Some liquid biofuels such as corn-based ethanol, mainly for transport, may aggravate rather than ameliorate carbon emissions on a life-cycle basis. Second generation biofuels, based on ligno-cellulosic feedstocks — such as straw, bagasse, grass and wood — hold the promise of sustainable production that is high-yielding and emit low levels of greenhouse gases, but these are still in the R & D stage.
With reference to the passage, following assumptions have been made :
- 1. Some climate-energy models suggest that the use of biomass as a fuel for power generation helps in mitigating greenhouse gas emissions
- 2. It is not possible to use biomass as a fuel for power generation without disrupting food and forest resources
Which of these assumptions is/are valid ?
Answer (a) & explanation
Only assumption 1 is valid (a). Step 1: the passage says climate-energy models rely on biomass for "negative emissions", and that it has "the highest mitigation potential". So some models do see biomass as helping to cut greenhouse gases. Assumption 1 holds. Step 2: assumption 2 says biomass power is impossible without disrupting food and forest. But the passage says a large potential exists "without disruption of food and forest resources". So 2 contradicts the passage. Step 3: so options (b), (c) and (d) fail.
Tip: when an assumption directly clashes with a quoted line, it is never valid. Look for the line that the statement contradicts.
Answer as per the official UPSC answer key.