Mental Maths

4 minQuiz at the end

Why Mental Maths Matters

Strong mental maths skills save time, help you check calculator answers, and build number confidence. The key is knowing which strategy to use for each type of calculation.

Key Strategies

Rounding and Adjusting (Compensation)

Round to a near number, calculate, then adjust:

  • 99 Γ— 7 = 100 Γ— 7 - 1 Γ— 7 = 700 - 7 = 693
  • 48 + 39 = 48 + 40 - 1 = 87

Doubling and Halving

Useful for multiplication:

  • 16 Γ— 25 = 8 Γ— 50 = 4 Γ— 100 = 400

Halving twice for division:

  • 64 Γ· 4 β†’ 64 Γ· 2 = 32, 32 Γ· 2 = 16

Partitioning

Break numbers into parts:

  • 34 + 58 = 30 + 50 + 4 + 8 = 80 + 12 = 92

Using Known Facts

Build from what you know:

  • 7 Γ— 8 = 56, so 7 Γ— 80 = 560 and 70 Γ— 8 = 560

Finding 10%, Then Scaling

  • 15% of 80: 10% = 8, 5% = 4, so 15% = 12
  • 25% = ΒΌ of the number: 25% of 80 = 80 Γ· 4 = 20

Quick Estimation

Round all numbers to 1 significant figure:

  • 49 Γ— 21 β‰ˆ 50 Γ— 20 = 1,000