Mental Maths Techniques for Competitive Exams

Seconds saved on calculation add up across a paper. These techniques are simple, reliable and quick to learn.

Multiply by splitting

To compute 23 × 14, do 23 × 10 = 230 and 23 × 4 = 92, then add: 322. Splitting one number into tens and units keeps the working in your head.

Square numbers ending in 5

For 35², multiply the tens digit by the next digit (3 × 4 = 12) and append 25, giving 1,225. The same works for 65² = 4,225.

Squares near 50

For 47², use (50 − 3)² = 2,500 − 300 + 9 = 2,209. The idea of working from a round number works for many squares.

Percentages from 10% and 1%

For 17% of 240, take 10% (24), 5% (12) and 2% (4.8): 24 + 12 + 4.8 = 40.8.

Estimate first

When options are far apart, estimate. 49 × 21 is roughly 50 × 20 = 1,000, which is enough to pick between 1,029 and 1,490.

Keep practising

Techniques only help if they become automatic. Practise daily with simplification sets and squares and cubes drills. A broader view of building speed is in improving speed and accuracy.