This is incorrect. It's 1 in ~50. Still bad!

8.5% of incoming freshmen place in Math 2. 25% of a class of Math 2 students could (EDIT: couldn't) answer 7+2=_+6

8.5% x 25% is about 2%, so 1 in 50.

Shouldn't that be 8.5% x 75% since you want the percent who could not answer it?