The 36-second budget: when to round and when to work exactly
The SSC notice for CHSL 2026 (para 13.8) gives each part of Tier I a sectional timer of 15 minutes for 25 questions: 36 seconds a question. A percent question fits that budget when you turn the percent into a friendly fraction first, and round only when the options are far enough apart for rounding to be safe.
Guess first
Guess first: about how much is 16.4% of ₹6,012? Pick in a few seconds.
Show answer
Correct answer: B
16.4% is close to 16⅔% = 1/6, and ₹6,012 is close to ₹6,000. 6,000 ÷ 6 = 1,000. The exact answer is 16.4% of 6,012 = 985.968, and no other option is anywhere near it.
Option A: ₹5,000 is the rest of ₹6,000 after taking 1/6 away (6,000 − 1,000 = 5,000), not the part asked.
Option C: ₹100 is ten times too small: the decimal point slipped one place.
Option D: ₹360 divides 6,000 by 16⅔ (6,000 ÷ 16⅔ = 360). A percent of a number is a share of it, not a division by the percent.
Hint: Which fraction is close to 16.4%?
If you picked ₹1,000 without writing anything down, you used the two habits of this lesson: a friendly fraction, and a look at the options before working.
An everyday picture
Rounding in the exam works like paying at a shop counter.
A bill of ₹487, and you hold notes of ₹100, ₹200 and ₹500 far apart
"about ₹500" is enough to choose the note
The same bill, and the shopkeeper counts your ₹13 change close
here every rupee is counted exactly
Exam options far apart, or close together the same choice
round when they are far apart, work exactly when they are close
The options in a question are your notes on the counter: they tell you how exact you need to be.
See it: the budget and the friendly fractions
The notice gives a sectional timer for each part. Your pace:
| Who | Time for a 25-question part | Per question |
|---|---|---|
| Most candidates | 15 minutes = 900 seconds | 900 ÷ 25 = 36 seconds |
| Candidates eligible for a scribe | 20 minutes = 1,200 seconds | 1,200 ÷ 25 = 48 seconds |
A friendly fraction turns a percent into one division:
| Percent near | Exact percent | Fraction |
|---|---|---|
| 16.7% | 16⅔% | 1/6 |
| 14.3% | 14 2/7% | 1/7 |
| 12.5% | 12.5% | 1/8 |
| 11.1% | 11 1/9% | 1/9 |
| 9.1% | 9 1/11% | 1/11 |
| 6.25% | 6.25% | 1/16 |
flowchart TD
A["Read the four options first"] --> B{"Are the nearest two far apart?"}
B -->|"yes"| C["Round to a friendly fraction and pick the nearest option"]
B -->|"no, close together"| D["Work exactly: multiply or use the exact fraction"]
C --> E["Check the size: less than the whole for a percent under 100%"]
D --> E
Try it. In the 60-minute paper you have used 22 minutes and finished 40 questions. At 36 seconds a question, are you ahead of the pace or behind it, and by how many minutes?
Find the rule
About how much is 12.6% of 7,190?
Show answer
Correct answer: C
12.6% is close to 12.5% = 1/8, and 7,190 is close to 7,200. 7,200 ÷ 8 = 900. The exact answer is 12.6% of 7,190 = 905.94, and every other option is far from it.
Option A: 6,300 is the rest of 7,200 (7,200 − 900 = 6,300), not 12.5% of it.
Option B: 90 is ten times too small: the decimal point slipped one place.
Option D: 576 divides 7,200 by 12.5 (7,200 ÷ 12.5 = 576), not a share of 7,200.
Hint: 12.5% is one eighth.
A candidate eligible for a scribe gets 20 minutes for each 25-question part. How many seconds is that per question?
Show answer
Correct answer: A
20 minutes = 20 × 60 = 1,200 seconds, and 1,200 ÷ 25 = 48 seconds a question.
Option B: 0.8 divides the minutes, not the seconds (20 ÷ 25 = 0.8): that is 0.8 of a minute.
Option C: 12 seconds shares the part's 1,200 seconds among all 100 questions of the paper (1,200 ÷ 100 = 12).
Option D: 1.25 turns the division upside down (25 ÷ 20 = 1.25).
Hint: Change the minutes to seconds first.
Find 11.2% of 2,250. Two of the options, 250 and 252, are very close, so work exactly.
Show answer
Correct answer: D
2,250 × 0.112 = 252. Rounding 11.2% to 11 1/9% = 1/9 gives 2,250 ÷ 9 = 250: a move of 2, as big as the gap between the two close options, so here rounding cannot decide.
Option A: 25.2 is ten times too small: the decimal point slipped one place.
Option B: 1,998 is the rest of 2,250 (2,250 − 252 = 1,998), not 11.2% of it.
Option C: 250 is 1/9 of 2,250, the answer for 11 1/9%, not for 11.2%.
Hint: When two options are this close, multiply exactly: 2,250 × 0.112.
Name the rule
- Your budget: 15 minutes for 25 questions is 36 seconds a question (48 seconds for candidates eligible for a scribe, who get 20 minutes a part).
- Friendly fractions: near 16⅔% use 1/6, near 14 2/7% use 1/7, near 12.5% use 1/8, near 11 1/9% use 1/9, near 9 1/11% use 1/11, near 6.25% use 1/16.
- Round only when it is safe: a rounding moves the answer a little. When the two nearest options are further apart than that move, round; when they are closer, work exactly.
- Check the size: a percent under 100% of a number is less than the number.
Exact work on 16.4% of 6,012 takes several steps; 1/6 of 6,000 takes one. Over 25 questions, the seconds you save on the easy estimates pay for the hard questions.
Worked, half-done, solo
Question
About how much is 9.1% of 3,289? The options are 300, 330, 360 and 390.
Solution
- Read the options first
They are 30 apart, so a small rounding cannot change the choice.
- Pick the friendly fraction
9.1% is close to 9 1/11% = 1/11, and 3,289 is close to 3,300.
- Divide once
3,300 ÷ 11 = 300.
- Check that the rounding was small
The exact answer is 9.1% of 3,289 = 299.299, far closer to 300 than to 330.
Answer: 300
Watch out: Rounding 9.1% up to 10% gives 10% of 3,289 = 328.9, closest to 330: a whole percent is too big a jump here.
Now finish one that is half done.
About how much is 14.2% of 4,903? Rounded: 14.2% is close to 14 2/7% = 1/7, and 4,903 is close to 4,900. Finish it.
Show answer
Correct answer: B
4,900 ÷ 7 = 700. The exact answer is 14.2% of 4,903 = 696.226, and the other options are far away.
Option A: 4,200 is the rest of 4,900 (4,900 − 700 = 4,200), not the part asked.
Option C: 70 is ten times too small: the decimal point slipped one place.
Option D: 343 divides 4,900 by 14 2/7 (4,900 ÷ 14 2/7 = 343).
Hint: Divide 4,900 by 7.
And one on your own.
About how much is 6.3% of 1,593?
Show answer
Correct answer: C
6.3% is close to 6.25% = 1/16, and 1,593 is close to 1,600. 1,600 ÷ 16 = 100. The exact answer is 6.3% of 1,593 = 100.359.
Option A: 1,500 is the rest of 1,600 (1,600 − 100 = 1,500), not 6.25% of it.
Option B: 10 is ten times too small: the decimal point slipped one place.
Option D: 256 divides 1,600 by 6.25 (1,600 ÷ 6.25 = 256).
Hint: 6.25% is one sixteenth.
The traps
- Rounded when the options were close: look at the options before you round.
- Rounded to a whole percent: 9.1% to 10% is a big jump; 9 1/11% = 1/11 is a small one.
- Rounded both numbers the same way: rounding the percent up and the number up makes the error bigger.
- Mixed minutes and seconds: 20 minutes for 25 questions is 48 seconds, not 0.8.
- Stayed too long: a question that has taken two or three times your 36 seconds is better left, and taken up again if time remains in the part.
Kunal must find 9.4% of 4,180. Two of the four options are 393 and 404. He estimates 10% of 4,200 = 420. What should he do?
Show answer
Correct answer: A
His rounding moved the answer by 420 − 392.92 = 27.08, more than the gap of 404 − 393 = 11 between the two close options, so the estimate cannot choose. Working exactly: 4,180 × 0.094 = 392.92, so 393.
Option B: Both numbers were rounded up, 9.4% to 10% and 4,180 to 4,200, so the errors added up instead of cancelling.
Option C: 400 lands nearer 404, the wrong option: when options are close, rounding in either direction can mislead.
Option D: Dividing by the percent does not give a share of the number.
Hint: Compare how far the rounding moves the answer with the gap between the close options.
Mixed check
About how much is 20.3% of 2,470?
Show answer
Correct answer: D
20.3% is close to 20% = 1/5, and 2,470 is close to 2,500. 2,500 ÷ 5 = 500. The exact answer is 20.3% of 2,470 = 501.41.
Option A: 2,000 is the rest of 2,500 (2,500 − 500 = 2,000), not 20% of it.
Option B: 50 is ten times too small: the decimal point slipped one place.
Option C: 125 divides 2,500 by 20 (2,500 ÷ 20 = 125).
Hint: 20% is one fifth.
From lesson 9:
A shop cuts the price of a fan by 20% and sells 15% more fans. By what percent do its takings from fans change?
Show answer
Correct answer: B
Strips: −20 + 15 = −5 squares. Corner: 20 × 15 ÷ 100 = 3 squares, taken away because one change is a fall. −5 − 3 = −8: the takings fall 8%. Check: 0.8 × 1.15 = 0.92.
Option A: A 5% decrease adds the percents and forgets the corner.
Option C: A 2% decrease adds the corner back (−5 + 3 = −2) instead of taking it away.
Option D: A 3% decrease is only the corner; the strips are missing.
Hint: One change is a fall. Is the corner added or taken away?
Quick reference
The 36-second budget
- Time per question
- the part's seconds ÷ its 25 questions 900 ÷ 25 = 36 seconds; with a scribe 1,200 ÷ 25 = 48 seconds
- Friendly fractions
- 1/6, 1/7, 1/8, 1/9, 1/11, 1/16 16.4% of 6,012: about 6,000 ÷ 6 = 1,000
- When to round
- the nearest options are further apart than the rounding moves the answer options 30 apart: round; options 2 apart: work exactly
- Check the size
- under 100% means less than the whole 6.3% of 1,593 is about 100, far below 1,593
Why it works: a friendly fraction turns a percent into one division, and the options tell you how exact you have to be.
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