Exam Hall 1: Your 36-second budget and smart rounding
This module trains exam behaviour, not new maths. Keep a timer next to you and give each check about 30 seconds.
60-second refresher: the basics
Speed is built on the basics. Read this once slowly; in the exam it must be automatic.
1. What is a percent? "Per cent" means per hundred. 35% means 35 out of every 100. Think of ₹100 as 100 coins of ₹1. If you spend 35 of the coins, you spent 35 out of 100, which is 35% of your money. On a 100-square grid each square is 1%, so 35% is 35 shaded squares:
███████████████████████████████████·································································
Text version: 35 of the 100 squares are shaded (35%); 65 are not (65%).
2. What does "of" mean? "Of" tells you which thing the percent is taken from. "35% of ₹200" means: cut ₹200 into 100 equal pieces (each piece is ₹200 ÷ 100 = ₹2) and take 35 pieces: 35 × ₹2 = ₹70.
3. Whole and part. The number after "of" is the whole: all of it, 100%. A part is a piece of the whole. The rest is what is left: whole − part, which is (100 − percent)%. In the example: whole ₹200, part ₹70 (35%), rest ₹130 (65%).
4. The one tool you will use in every question: find 1% first. 1% of anything = that thing ÷ 100. From 1% you can build any percent (multiply by the percent) or get back to the whole (multiply by 100). Try it now: 1% of ₹300 = 300 ÷ 100 = ₹3, so 35% of ₹300 = 35 × 3 = ₹105.
Words to know
- Percent (%)
- out of every 100 35% = 35 out of 100
- Whole
- the number after 'of' = 100% ₹200 in '35% of ₹200'
- Part
- a piece of the whole ₹70 = 35% of ₹200
- Rest
- whole − part ₹130 = 65% of ₹200
- 1%
- whole ÷ 100 1% of ₹200 = ₹2
Drill 1: know your budget
CHSL Tier-I gives each part 25 questions with a 15-minute sectional timer. How many seconds is that per question?
Show answer
Correct answer: B
900 s ÷ 25 = 36 s per question, about 30 s if you keep a short buffer for review.
Option A: Guessed: 60 s would need 25 minutes.
Option C: Wrong total time: 24 s would mean only 10 minutes for 25 questions.
Option D: Unit conversion slip: 15 ÷ 25 = 0.6 is in minutes, not seconds.
Hint: Convert minutes to seconds first.
CHSL 2026 Tier-I facts (official notice, 7 Sep 2026)
- Quant part
- 25 questions, 50 marks 2 marks each
- Time
- 15-minute sectional timer per part 36 s per question
- Negative marking
- −0.50 per wrong answer 4 wrong = −2
Scribe-eligible candidates get 20 minutes per part. Check the latest notice before your exam.
Drill 2: round to friendly numbers
Approximate: 33.2% of 151 is closest to
Show answer
Correct answer: D
Round to a friendly fraction and a friendly number: 1/3 of 150 = 50.
Option A: Over-rounded: 45 is 30% of 150.
Option B: Over-rounded: 55 is about 36.7% of 150.
Option C: Decimal slip: 5 is 3.3% of 150: decimal slip.
Hint: 33.2% is close to which fraction?
When rounding is safe
- Look at the options first. If they are far apart (like 45, 50, 55), round freely.
- If two options are close (like 79 and 80), compute exactly.
- Round one number up and the other down when you can: the errors cancel.
Solve one slowly, then fast
Question
About how much is 19.6% of ₹501? Options: ₹80, ₹98.20, ₹110, ₹120.
Solution
- What is the question asking?
- ₹501 is the whole (100%). We need 19.6% of it: a part of ₹501.
- The options are far apart (about ₹10 or more), so a close estimate is enough.
- Make it a story
- Five friends share a ₹501 dinner bill. Your share is 19.6% of the bill.
- We know / We need
- We know: 100% of the bill = ₹501
- We need: 19.6% of the bill ≈ ?
- Step 1: find 1% (rounded)
- 1% of the bill = 501 ÷ 100 = ₹5.01 ≈ ₹5
- Step 2: find about 20%
- 19.6% is very close to 20%.
- 20% of the bill ≈ 20 × ₹5 = ₹100
- See it on a bar
████░░░░░░░░░░░░░░░░each block = 5% of the bill (about ₹25)- █ about 20% ≈ ₹100 (your share)
- ░ about 80% ≈ ₹400 (the others)
- Whole bar = 100% = ₹501
- Shortcut (only after you understand)
- Round both numbers to friendly ones: 20% of 500 = 100.
- If two options were close, work it exactly: 19.6 × 5.01 = 98.196 ≈ ₹98.20.
- Quick check
- Only ₹98.20 is near ₹100 ✓
- We rounded 19.6% up to 20%, so the true answer is a little BELOW ₹100 ✓
Answer: ₹98.20
Watch out: Most important concept: Round only when the options are far apart. The percent is still a percent of the bill (₹501): find 1% of the bill first, then scale.
Test your understanding: about how much is 24.8% of 801?
Show answer
Correct answer: B
We need 24.8% of 801, a part of 801. Step 1: 1% of 801 ≈ 8 (round 801 to 800). Step 2: 24.8% ≈ 25%, so about 25 × 8 = 200. The options are far apart, so the estimate is safe. Exact: 0.248 × 801 = 198.65.
Option A: Decimal slip: About 20 is 2.5% of 801: the decimal moved one place too far.
Option C: Answered the remainder: About 600 is the other 75% of 801, not the 25% asked for.
Option D: Rounded too far: About 250 rounds 801 all the way up to 1,000. Round to the nearest friendly number (800), not a far one.
Hint: 25% is one quarter. Round 801 to 800.
Know these cold: 1/3 = 33.3%, 1/6 = 16.7%, 1/7 ≈ 14.3%, 1/8 = 12.5%, 1/9 ≈ 11.1%, 1/11 ≈ 9.1%, 1/12 ≈ 8.3%.
Five questions are attached below. Time yourself: aim for under 3 minutes in total.
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