Question

When Professor Sum was asked by Mr. Little how many students were in his classes, he answered, “All of them study either languages, physics, or not at all. One-half of them study languages only, one-fourth of them study French, one-seventh of them study physics only, and 20 do not study at all.” How many students does Professor Sum have?

Answer 1

1/2 + 1/4 + 1/7 = X - 20

Solve for X.

I hope this helps.