selvae wrote:

A group contains 7 boys and some girls. The number of teams of 5 comprising 3 boys and 2 girls is 525. How many girls are in the group?

5

6

7

9

11

boys=> 7!/4!3!=35

525=35*g, where g is the number of teams comprising of girls only, so g=525/35=15 girls

We know that 15 = g!/(g-2)!2! , where g is the total number of girls available.

Solving backwards, and plugging the 1st available answer 5 quickly shows us that the number of girls should be a bit higher. Trying the number 6 works: 6!/4!2!=15

So, the answer is B.