Splitting a factor
Split a factor into tens and units, multiply each part, then add them up.
14 × 12 = 168
- 10 × 12 = 120
- 4 × 12 = 48
- 120 + 48 = 168
Mental math techniques
Tricks to calculate faster in your head, sorted by level. Each one comes with a worked example, step by step.
Level 3 · Hard 5 techniques
Multiplying by 25
25 is 100 ÷ 4: multiply by 100, then divide by 4.
16 × 25 = 400
- 16 × 100 = 1600
- 1600 ÷ 4 = 400
Dividing by 5
÷ 5 is × 2, then ÷ 10.
135 ÷ 5 = 27
- 135 × 2 = 270
- 270 ÷ 10 = 27
Squaring a number ending in 5
Multiply the tens digit by the next number, then write 25 at the end.
35² = 1225
- 3 × 4 = 12
- 12 × 100 + 25 = 1225
Dividing in two steps
A divisor that splits up (6 = 2 × 3) can be done as two easy divisions. Divisibility rules (even, sum of digits…) tell you where to start.
168 ÷ 6 = 28
- 168 ÷ 2 = 84
- 84 ÷ 3 = 28