Show WorkingWorked example 1: substitute into an expression
Work out the value of 5x + 5 when x = 1.
- Replace x with 1: 5 × 1 + 5.
- Multiply first: 5 × 1 = 5.
- Then add: 5 + 5 = 10.
Answer 10
AlgebraFoundation and Higher
Substitution: GCSE maths practice with worked answers
Show Working has 2 kinds of substitution question for GCSE Maths, for Foundation and Higher. Every question is new each time and comes with the working, step by step.
Substitution means putting numbers in place of letters and working out the value of an expression. GCSE questions often use negative numbers and powers, which is where most marks are lost.
Coming soon to the App Store01 / What's covered2 kinds of question
Substitution questions in the app
Each kind makes fresh questions every time, so you can practise as often as you like.
- Substitute into an expressionBoth tiers
- Substitute with powers and negativesBoth tiers
Worked example 2: substitute with powers and negatives
Work out the value of 4x2 − 8 when x = −6.
- Replace x with (−6): 4 × (−6)² − 8.
- Square first: (−6)² = (−6) × (−6) = 36. A negative number times a negative number is positive.
- Multiply by 4: 4 × 36 = 144. Then subtract: 144 − 8 = 136.
Answer 136
A common mistake
Squaring a negative number without brackets. When x = −6, x² means (−6)² = 36, not −36.
02 / Practise itiPhone and iPad
Practise substitution in Show Working
In the app, open Topics and choose Substitution for ten fresh questions. Ask for a hint if you are stuck, and open the working to see the method one step at a time.
Coming soon to the App Store