math
posted by james on .
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. Onehalf of them study languages only, onefourth of them study French, oneseventh of them study physics only, and 20 do not study at all.” How many students does Professor Sum have?

1/2 + 1/4 + 1/7 = X  20
Solve for X.
I hope this helps.