A reading list for humanities course consists of 10 books, of which 4 are biographies and the rest are novels. Each student is required to read a selection of 4 books from the list, including 2 or more biographies. How many selections of 4 books satisfy the requirements?

Answer 1

There are 4C2 = 6 ways to choose the two required biographies.

That leaves 8 other books, with 8C2 = 28 ways to pick them.

So, there are 6*28 = 168 ways to pick 4 books as required.

Answer 2

115