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Fast calculation techniques for SSC CGL

In a section with 36 seconds per question, calculation speed matters as much as concepts. You don't need "Vedic maths magic" — you need a handful of reliable techniques: squares near 50 and 100, multiplying by 5, 25 and 11, percentage shortcuts, digit-sum checks and smart approximation. What to memorise, which tricks are worth learning, a 20-minute daily drill, and practice with answers.

14 Oct 2026 3 min read

In this guide
  1. What to memorise
  2. Multiplication shortcuts
  3. Squares
  4. Division and fractions
  5. Percentage shortcuts
  6. Checking answers with digit sums
  7. Approximation
  8. A 20-minute daily drill
  9. Practice

Two candidates know exactly the same method for a profit-and-loss question. One multiplies 1.25 × 0.88 in five seconds; the other writes it out and takes twenty-five. Across a paper, those twenty-second gaps add up to several questions. Calculation speed isn't talent. It is a small set of memorised facts and simple techniques, practised daily until they become automatic.

What to memorise

ItemRange
Multiplication tablesUp to 20
SquaresUp to 30 (ideally 50)
CubesUp to 15
Square roots√2 ≈ 1.414, √3 ≈ 1.732, √5 ≈ 2.236
Fraction–percentage equivalents1/2 to 1/20

Multiplication shortcuts

Multiplying by 5, 25 and 125

  • × 5 = × 10 ÷ 2 → 468 × 5 = 4,680 ÷ 2 = 2,340.
  • × 25 = × 100 ÷ 4 → 64 × 25 = 6,400 ÷ 4 = 1,600.
  • × 125 = × 1,000 ÷ 8 → 48 × 125 = 48,000 ÷ 8 = 6,000.

Multiplying by 11

For a two-digit number, write the two digits with their sum in between (carrying if needed).

  • 34 × 11 → 3 (3 + 4) 4 = 374.
  • 78 × 11 → 7 (15) 8 → carry the 1 → 858.

Multiplying by 9, 99 and 999

  • 47 × 99 = 47 × 100 − 47 = 4,653.

Numbers near 100

To multiply 97 × 94: the deficits from 100 are 3 and 6.
Cross-subtract: 97 − 6 = 91. Multiply the deficits: 3 × 6 = 18. Answer: 9,118.

For 104 × 107: surpluses 4 and 7. 104 + 7 = 111; 4 × 7 = 28. Answer: 11,128.

Squares

Numbers ending in 5

For n5², multiply n by (n + 1) and append 25.

  • 65² → 6 × 7 = 42 → 4,225.
  • 115² → 11 × 12 = 132 → 13,225.

Numbers near 50

For (50 + a)² = 2,500 + 100a + a².

  • 53² = 2,500 + 300 + 9 = 2,809.
  • 47² = 2,500 − 300 + 9 = 2,209.

Using (a + b)²

  • 104² = 10,000 + 800 + 16 = 10,816.

Division and fractions

  • Divide by 5 by multiplying by 2 and shifting the decimal: 365 ÷ 5 = 73.
  • Compare fractions by cross-multiplying: 7/9 vs 11/14 → 7 × 14 = 98 and 11 × 9 = 99, so 11/14 is larger.

Percentage shortcuts

  • 18% of 450 = 10% (45) + 8% (36) = 81.
  • x% of y = y% of x: 16% of 25 = 25% of 16 = 4.
  • Successive percentages: × 1.2 × 0.9 = × 1.08 → an 8% net increase.

Checking answers with digit sums

The digit sum (repeated until one digit) of a product equals the digit sum of the product of the factors' digit sums.

Check 47 × 23 = 1,081: digit sums 4 + 7 → 11 → 2, and 2 + 3 = 5. 2 × 5 = 10 → 1. For 1,081: 1 + 0 + 8 + 1 = 10 → 1. ✓

This quickly eliminates wrong options in simplification questions.

Approximation

  • Round to convenient numbers and adjust: 49.7 × 20.2 ≈ 50 × 20 = 1,000.
  • Check how close the options are before choosing how precisely to calculate.

A 20-minute daily drill

MinutesDrill
0–520 multiplications (2-digit × 2-digit)
5–1010 squares and 5 cubes from memory
10–1510 percentage calculations
15–205 simplification questions from previous papers

Track your time weekly. Most candidates see a clear improvement within a month.

Practice

  1. 76 × 25
  2. 67 × 11
  3. 96 × 93
  4. 85²
  5. 58²
  6. Which is larger: 5/7 or 8/11?
  7. 24% of 350

Answers: 1. 1,900. 2. 737. 3. 8,928. 4. 7,225. 5. 3,364. 6. 8/11 (5 × 11 = 55 < 8 × 7 = 56). 7. 84.

A note on dates and numbers. Exam patterns, vacancies and schedules change from year to year. Always confirm the current details in the latest notification on the Staff Selection Commission website .

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