Question

Find the ratio of the students who study French to students who do not study French give your answer in its simplest form

Answer 1

(2/5) of (2/3) of students = 4/15 of students study French. Then 1-(4/15) = 11/15 of students do not study French. The ratio you want is
  (4/15):(11/15) = 4:11

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In a math expression "of" means "times".