A theater had 100 people in the audience consisting of men, women, and children. The prices of the tickets were $10 for men, $3 for women, and $0.50 for children. The theater collected a total of $100 from 100 people.
How many men, women, and children were in the audience?

There are two possible answers.

Let M = number of men, W = number of women, and C = number of children. Hint: think of M as a constant (not a variable) leaving two equations in two unknowns W and C, and solve for these unknowns - i.e. get W as a function of M. You'll see that since M and W must both be integers that M is limited to just three possibilities, only two of which make sense.