Maths Tricks for Faster Calculations

Multiplying by 11

Example: 34 × 11 → Add digits: 3 + 4 = 7 → Result: 374

Multiplying by 9

Use fingers for 1–10, or subtract 1 from the number and write the complement: Example: 7 × 9 → 7–1 = 6 → 9–6 = 3 → Result: 63

Square of numbers ending with 5

Example: 25² → Multiply first digit by (first digit +1): 2×3=6 → Add 25 at end → 625

Adding large numbers

Round up and adjust. Example: 398 + 276 → 400 + 276 = 676 → Subtract 2 → 674

Subtracting from 1000

Subtract each digit from 9 except the last digit from 10. Example: 1000 – 186 → (9–1 = 8, 9–8 = 1, 10–6 = 4) → 814

Dividing by 5

Multiply by 2 and divide by 10. Example: 245 ÷ 5 → 245×2=490 → 490 ÷ 10 = 49

Divisibility rules

By 2: Last digit even By 3: Sum of digits divisible by 3 By 4: Last 2 digits divisible by 4 By 5: Last digit 0 or 5 By 9: Sum of digits divisible by 9

Square of numbers near 50

Example: 97² Difference from 100 = 3 Subtract 3 from 97 → 94 Square the difference (3² = 9) Answer = 9409 so,97² = 9409

Cube of numbers ending with 5

Example: 25³ → (2×3)=6 → Add 125 → 6 125 → 15625

Distributive method

Example: 23 × 47 → (20+3)(40+7) = 20×40 + 20×7 + 3×40 + 3×7 = 940 + 140 + 120 + 21 = 1221

Quick 10%, 5%, 1%

10% → divide by 10 5% → divide by 2 after 10% 1% → divide by 100

Fraction to percentage

Multiply fraction by 100. Example: 5/12 Multiply numerator by 100 -> 5×100 = 500 Divide by denominator → 500 ÷ 12 = 41.66 Answer = 41.67% (approx.) so, 5/12 = 41.67%​

Day of the week

Use simple formulas like Zeller’s Rule (for practice).

Leap years

Year divisible by 4 (except century not divisible by 400).

Multiplying by 4

Multiply by 2 twice

Multiplying by 8

Multiply by 2 three times

Speed addition of consecutive numbers

n(n+1)/2 formula