Theory & Concepts

SSC CGL Approximation and Rounding Questions & Tricks

Get comprehensive theory, expert shortcuts, and hand-picked practice questions for Approximation & Rounding specifically designed for the SSC CGL 2025-26 pattern.

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20 min readDifficulty: Easy-Intermediate

Approximation is a survival skill in SSC CGL, especially for Data Interpretation (DI) and long arithmetic calculations. Instead of wasting time finding exact decimal points, rounding numbers intelligently to their nearest comfortable values will lead you to the exact answer option in seconds.

Learning path

  • Standard Rounding Rules
  • The 10% & 1% Shift Hack
  • Fraction Equivalents
  • 10 Exam-Level Examples

1. Standard Rounding Rules

In competitive exams, any decimal value ending with .01 to .49 is rounded down, and .50 to .99 is rounded up.

Rounding Up

14.89≈1514.89 \approx 15

399.98≈400399.98 \approx 400

11.51≈1211.51 \approx 12

Rounding Down

14.12≈1414.12 \approx 14

400.05≈400400.05 \approx 400

11.45≈1111.45 \approx 11

2. The Decimal Shift Hack

Never calculate percentages manually. Shift the decimal to instantly find 10% and 1% of any number.

Percentage Construction

To find 11% of 850:

1. Find 10%: Shift decimal left by 1. 10%=85.010\% = 85.0

2. Find 1%: Shift decimal left by 2. 1%=8.51\% = 8.5

3. Add them: 11%=85+8.5=93.511\% = 85 + 8.5 = 93.5

Use this to easily construct approximations like 21% (10% + 10% + 1%) or 9% (10% - 1%).

3. Fraction Equivalents

Examiners often hide clean fractions behind messy percentage decimals. Memorize these reversals:

Thirds & Sixths

33.33%≈1/333.33\% \approx 1/3

66.66%≈2/366.66\% \approx 2/3

16.66%≈1/616.66\% \approx 1/6

83.33%≈5/683.33\% \approx 5/6

Sevenths & Ninths

14.28%≈1/714.28\% \approx 1/7

28.56%≈2/728.56\% \approx 2/7

11.11%≈1/911.11\% \approx 1/9

9.09%≈1/119.09\% \approx 1/11

4. 10 Solved examples

Question 01Exam Pattern

Find the approximate value of \( 45.09 \times 11.98 - 35.88 \).

480
504
520
544
Correct answer: b) 504

Solution

Step 1: Round the numbers to the nearest integers.
Step 2: \( 45.09 \approx 45 \).
Step 3: \( 11.98 \approx 12 \).
Step 4: \( 35.88 \approx 36 \).
Final calculation: \( 45 \times 12 - 36 = 540 - 36 = 504 \).
Question 02Exam Pattern

What is the approximate value of \( 12.03\% \text{ of } 849.99 \)?

85
102
110
120
Correct answer: b) 102

Solution

Step 1: Round the values: \( 12\% \text{ of } 850 \).
Step 2: Use the decimal shift hack.
Step 3: 10% of 850 = 85.
Step 4: 1% of 850 = 8.5. So, 2% = 17.
Final calculation: \( 10\% + 2\% = 85 + 17 = 102 \).
Question 03Exam Pattern

Find the approximate value: \( \frac{347.99}{11.98} + \sqrt{143.9} \).

38
41
44
47
Correct answer: b) 41

Solution

Step 1: Round the numbers to their nearest calculation-friendly integers.
Step 2: The fraction becomes \( \frac{348}{12} \).
Step 3: The square root becomes \( \sqrt{144} \).
Step 4: Perform the division: \( 348 \div 12 = 29 \).
Step 5: Perform the square root: \( \sqrt{144} = 12 \).
Final calculation: \( 29 + 12 = 41 \).
Question 04Exam Pattern

Find the approximate value: \( \sqrt[3]{511.98} + \sqrt{63.98} \).

12
14
16
18
Correct answer: c) 16

Solution

Step 1: Identify the nearest perfect cube and perfect square.
Step 2: Nearest perfect cube to 511.98 is 512 (which is \( 8^3 \)).
Step 3: Nearest perfect square to 63.98 is 64 (which is \( 8^2 \)).
Step 4: Evaluate the roots: \( \sqrt[3]{512} = 8 \) and \( \sqrt{64} = 8 \).
Final calculation: \( 8 + 8 = 16 \).
Question 05Exam Pattern

Evaluate: \( (14.99)^2 - (4.98)^2 \).

200
225
150
250
Correct answer: a) 200

Solution

Step 1: Round the values: \( 15^2 - 5^2 \).
Step 2: You can calculate directly or use the identity \( a^2 - b^2 = (a+b)(a-b) \).
Step 3: Direct: \( 225 - 25 = 200 \).
Step 4: Using identity: \( (15+5)(15-5) = 20 \times 10 = 200 \).
Final calculation: Result = 200.
Question 06Exam Pattern

Find the approximate value: \( 33.31\% \text{ of } 1206 + 16.67\% \text{ of } 240 \).

430
442
450
462
Correct answer: b) 442

Solution

Step 1: Recognize the decimal equivalents of fractions.
Step 2: \( 33.31\% \approx \frac{1}{3} \).
Step 3: \( 16.67\% \approx \frac{1}{6} \).
Step 4: Substitute into the expression: \( \frac{1}{3} \times 1206 + \frac{1}{6} \times 240 \).
Step 5: Simplify: \( 402 + 40 \).
Final calculation: \( 402 + 40 = 442 \).
Question 07Exam Pattern

Simplify: \( \frac{124.99 \times 7.98}{24.98} \).

20
30
40
50
Correct answer: c) 40

Solution

Step 1: Round the numbers: \( \frac{125 \times 8}{25} \).
Step 2: Instead of multiplying the numerator first, simplify the fraction to save time.
Step 3: Divide 125 by 25. \( 125 \div 25 = 5 \).
Final calculation: \( 5 \times 8 = 40 \).
Question 08Exam Pattern

Find the approximate value: \( (6.01)^3 - (3.99)^3 \).

122
142
152
162
Correct answer: c) 152

Solution

Step 1: Round the base values: \( 6^3 - 4^3 \).
Step 2: Calculate the cubes.
Step 3: \( 6^3 = 216 \).
Step 4: \( 4^3 = 64 \).
Final calculation: \( 216 - 64 = 152 \).
Question 09Exam Pattern

Evaluate: \( \frac{15.98 \times 14.02}{7.99} \).

24
26
28
30
Correct answer: c) 28

Solution

Step 1: Round the values: \( \frac{16 \times 14}{8} \).
Step 2: Cancel out the common terms before multiplying.
Step 3: \( 16 \div 8 = 2 \).
Final calculation: \( 2 \times 14 = 28 \).
Question 010Exam Pattern

Approximate: \( 24.9\% \text{ of } 119.9 + 15.1\% \text{ of } 199.9 \).

50
60
70
80
Correct answer: b) 60

Solution

Step 1: Round the percentages and the bases: \( 25\% \text{ of } 120 + 15\% \text{ of } 200 \).
Step 2: \( 25\% \) is \( \frac{1}{4} \). So, \( \frac{1}{4} \times 120 = 30 \).
Step 3: \( 15\% \) of 200. Since 10% is 20 and 5% is 10, \( 20+10 = 30 \).
Final calculation: \( 30 + 30 = 60 \).

5. Strategy errors to avoid

!

Over-Rounding Early

Don't round numbers too aggressively in the middle of a calculation. For example, rounding 14.4 to 10 is dangerous. Keep it close to 14 or 15 to maintain accuracy for the final answer choice.

!

Ignoring the Options

Always look at the options first. If the options are very close (e.g., 502, 504, 506), you need to be very precise with your rounding. If they are far apart (e.g., 400, 500, 600), you can round much more loosely.

Master the next modules

Simplification (BODMAS)Surds & IndicesAverages