Round & adjust

49 × 6? Do 50 × 6, then fix it.

Most "hard" mental math is an easy problem in disguise. People who are quick with numbers don’t grind through 49 × 6. They do 50 × 6 and correct.

The move

Round one number to something friendly (a multiple of 10 or 100), multiply, then add or subtract the bit you rounded away, multiplied too.

Worked example

49 × 6

  1. 49 is 50 − 1
  2. 50 × 6 = 300
  3. The 1 you borrowed, times 6 = 6
  4. 300 − 6 = 294
  • Prices like $49, $99, $199 are begging for this move.
  • The classic slip is forgetting to multiply the correction. It’s 1 × 6, not just 1.