A political commentator summed up an election result. Given that
there were just four candidates and that the figures quoted were
exact find the number of votes polled for each candidate.
Problem one was solved by 70% of the pupils. Problem 2 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?
Weekly Problem 43 - 2013