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?

1 answer

Professor Sum has 56 students.
28 of then study languages - one half
(14 of which study French)
8 study physics - one-seventh
20 do not study at all.