Asked • 03/13/19

Intuition behind combination problem?

I came across this question on a GRE practice exam. I'm trying to build intuition behind how to correctly approach these types of problems: A reading list for a 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? Initially I thought you could solve the problem by finding out 4C2 (meaning choose 2 out of 4) and then group the remaining two biographies with the novels, leaving 8 books to choose from. Then I would solve for 8C2 to find out how many ways I could select the other 2 books from the remaining 8 and multiply that with the result from 4C2. Can somebody explain why my reasoning is wrong? Thank you.

2 Answers By Expert Tutors


Al P. answered • 09/20/19

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Alexander D. answered • 03/14/19

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