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Auralith Learning

Year 7 · Maths · Algebraic notation · Lesson 3

Substitution

Substitute numbers, including negatives and decimals, into expressions and formulas, using the order of operations.

Whiteboard video lesson: Substitution

23-minute video lesson

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

Watch free for a month

What your child will learn

  • Substitute into simple expressions
  • Use the order of operations
  • Substitute into expressions with brackets and powers
  • Substitute negative and decimal values
  • Use formulas

The method

  1. Write the expression.
  2. Replace each letter with its number.
  3. Put back hidden × signs: 3a = 3 × a.
  4. Use BIDMAS to work it out.

Key words: substitute, expression, formula, BIDMAS, value.

Worked examples

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

Question 1

Work out the value of n + 12 when n = 8.

  1. Step 1: n + 12
  2. Step 2: 8 + 12 = 20

Answer: 20

Question 2

Work out the value of 7y when y = 4.

  1. Step 1: 7y
  2. Step 2: 7 × 4 = 28

Answer: 28

Question 3

Work out the value of 20 − k when k = 6.

  1. Step 1: 20 − k
  2. Step 2: 20 − 6 = 14

Answer: 14