BajrangAssociate
Back to mental maths

Multiply by 5, 25, 125

Turn multiplication by 5/25/125 into multiplying by 10s and halving

The Rule

  1. 15 = 10 ÷ 2, 25 = 100 ÷ 4, 125 = 1000 ÷ 8 — powers of 5 are powers of 10 divided by the matching power of 2.
  2. 2Multiply the number by the power of 10 first (just add zeros).
  3. 3Then halve the result that many times — always comes out to a whole number.