The first fraction is between 27 and 28, closer to 28. The second fraction is between 3 and 4, closer to 4. Compatible numbers in division are numbers that can be divided mentally. 28 divided by 4 is 7. The quotient will be around 7.
(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
