Here is a number machine.
Input⟶×3⟶−7⟶Output \text{Input} \longrightarrow \times 3 \longrightarrow - 7 \longrightarrow \text{Output} Input⟶×3⟶−7⟶OutputFind the output when the input is 6
Find the input when the output is 20
84 exam-style questions on OCR GCSE Maths Function Machines. Each one has a worked solution and a mark scheme showing where the marks go.