A maths exam contained only two questions. Problem one was
solved by 70% of the pupils. Problem two was solved by 60% of
them. Every pupil solved at least one of the problems. Nine
pupils solved both problems. How many pupils took the exam?
In the following year the maths exam contained two percentage
problems. This time each problem was solved by 72% of the
pupils and every pupil got at least one problem right again.
What can you say about the number of pupils in the class?
Can you make a problem like this of your own?