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'One or Both' printed from http://nrich.maths.org/
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?