Hello, everyone. I was hoping you guys could help me out. I'm about to take this huge college entrance exam in two months and I bought this reviewer at a bookstore - the problem, however, is that the reviewer I bought only posts the ANSWERS to the questions without explanations.

How do you solve combination problems when they have specifications?

For example -

In how many ways can a comittee of five be chosen out of 15 people, 7 of which are males and 8 of which are females, if one male and one female are to be included in each selection?

(according to the answer key, the answer is 16,106)

or..

A shipment of 14 personal computers contains 4 defective units. In how many ways can a company purchase 5 of these units and receive at least 2 of the defective units?

(according to the answer key, the answer is 910)

any help would be great.