Here is a number machine.

Find the output when the input is 12
Find the input when the output is 13
Practise OCR GCSE Maths Function Machines with exam-style questions for Foundation and Higher tier. 39 questions, matched to the OCR GCSE Maths (J560) specification and written in the written papers style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.