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!(nr)!
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.