Help at home · Maths

How to explain substitution and brackets to your child

Put numbers in place of letters, e.g. 'If a = 4 and b = 3, what is 5a − 2b?', and sometimes multiply out brackets like 3(x + 2).

How schools teach it now

Year 6 uses simple formulae, such as perimeter = 2(l + w). Children swap each letter for its number (5a means 5 × a), then follow BODMAS. Multiplying out brackets is secondary work: everything inside is multiplied by the number outside.

5-minute kitchen-table activity

Make a snack price formula: a = an apple at 30p, b = a banana at 20p. 'What is 3a + 2b?' (90p + 40p = £1.30.) Then your child writes a formula for you to work out.

Worked example

If a = 4 and b = 3, what is 5a − 2b?

5a = 5 × 4 = 20.
2b = 2 × 3 = 6.
20 − 6 = 14.

Answer: 14

Common mistakes to watch for

Writing 5a as 54 by putting the digits side by side.
Treating a² as a × 2 instead of a × a.
In 3(x + 2), multiplying only the x: 3x + 2 instead of 3x + 6.

Encouragement

Try saying: “Swap each letter for its number. Then it's just a sum.”
Rather than: “Letters in maths are meant to be confusing.”

All Maths topics

Practise substitution and brackets with marked questions

Academy11+ marks every answer, shows how your child is doing in each topic and puts the right home-help note next to the ones they find hard.

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