Question

A math test is worth 100 points and has 30 problems. Each problem is worth either 3 points or 4 points. How many 4 point problems are there?

Answer 1

If you only have 3 point problems you have a total of 3*30=90 points, since the test has 100 points you need 10 extra points, so 10 of those 3 point questions have to be changed to 4 point questions.

So 20 3-point questions and 10 4-point questions.