Mike@Magoosh wrote:Hi, there. I'm happy to help with this.

First of all, I'll say: this question is unusual in form, because GMAT PS questions invariably have 5 answer choices. Also, the numbers seem a bit smaller and simpler than I've seen on analogous GMAT questions. Also, on the real GMAT, answer choices are almost always in numerical order. I am suspicious of the source of these questions.

A school has 3 classes, math class has 14 students. English class has 10 students, PE class has 11 students. That's a sum of 14 + 10 + 11 = 35. This sum counts "doublers" twice, and counts "triplers" three times.

There are 20 students taking only one class. Remove the singletons, 35-20 = 15, and that number represents the doublers counted twice and the triplers counted three times.

3 students are taking all three classes. There are three triplers, so they count for 9 in the total. 15 - 9 = 6, which represents the doublers counting twice. That means, there must be 3 doublers.

Answer = B

Does all this make sense? Please let me know if you have any questions on what I've said.

Mike