My teacher gave me this question to solve and I don't understand it at all.....Does anyone understand it or is the question wrong???
Liz and Mary compete in solving problems. Each of them is given the same list of 100 problems. For any problem, the first of them to solve it gets 4 points, while the second to solve it gets 1 point. Liz solved 60 problems, and Mary also solved 60 problems. Together they got 312 points. How many problems were solved by both of them?