A test consists of 20 problems and students are told to answer any 15 of these questions. In how many different ways can they choose the 15 questions?

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2016-04-21 09:55:38

1 - 15 2 - 17 3 - 18 4 - 19 5 - 20

2016-04-21 09:56:53

Since order is not important, we are looking for unique combinations. For this type of problem you use the "n choose k" equation. n!/(k!(n-k)!), where n=total amount of choices, k=number of choices made. In this case: 20!/(15!(20-15)!) 20!/(15!*5!) 15504

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