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Year 7 · Patterns & Algebra

Substitute into expressions

Substituting means replacing a letter with a number and working out the value.

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How to do it

  1. Write the expression with the number in place of the letter, in brackets.
  2. Multiply before adding.

Worked example

3x + 5 when x = 4
3 × 4 + 5 = 12 + 5
17

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Put negative numbers in brackets so the signs stay right.

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