GMATPREP:Do more students study French than Japanese?

Ian Stewart wrote:

vittalgmat wrote:Another nice one.

At least 100 students study Japanese. If 4% of students who study French also study Japanese, do more students study French than Japanese?
a. 16 students study both French and Japanese
b. 10% of students at school who study Japanese also study French

[spoiler]OA: B[/spoiler]

If F is the number who study French, and J the number who study Japanese, then using Statement 2 we know:

(4/100)*F = (10/100)*J
F = 2.5*J

so F is larger than J, and Statement 2 is sufficient.

Statement 1 allows us to work out that 400 students study French, but since we don't know how many study Japanese, the statement is insufficient.