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Year 6 · Maths · SATs revision · Lesson 6

Mental arithmetic strategies

Mental arithmetic strategies for SATs: near multiples, ×25, halving and doubling, partitioning, compensation and swapping percentages.

Whiteboard video lesson: Mental arithmetic strategies

19-minute video lesson

Teaching, worked examples and 20 practice questions solved step by step.

Watch free for a month

What your child will learn

  • Multiply using near round numbers
  • Use × 25 as × 100 ÷ 4
  • Halve and double
  • Partition to multiply
  • Use compensation to subtract

The method

  1. Look for a trick.
  2. Round, halve/double, or partition.
  3. Adjust if you rounded.
  4. Sense-check.

Key words: mental, partition, compensation, halve and double, round.

Worked examples

The first three practice questions from the lesson, with every step.

Question 1

Work out 6 × 99 in your head.

  1. Step 1: 99 = 100 − 1
  2. Step 2: 6 × 100 = 600
  3. Step 3: 600 − 6 = 594

Answer: 594

Question 2

Work out 8 × 31 in your head.

  1. Step 1: 31 = 30 + 1
  2. Step 2: 8 × 30 = 240
  3. Step 3: 240 + 8 = 248

Answer: 248

Question 3

Work out 12 × 19 in your head.

  1. Step 1: 19 = 20 − 1
  2. Step 2: 12 × 20 = 240
  3. Step 3: 240 − 12 = 228

Answer: 228