Posted by **Rena** on Tuesday, February 8, 2011 at 11:31pm.

How many combinations are there when you can buy four books from a choice of 6 books>

- Math -
**PsyDAG**, Wednesday, February 9, 2011 at 10:27am
Combinations = n!/r!(n-r)!

where n is the number of things to choose from, and you choose r of them

(No repetition, order doesn't matter)

5 factorial = 5! = 5 * 4 * 3 * 2 * 1 = 120

I'll let you do the calculations.

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