Math Is Fun Forum

Danbee

Member

Registered: 2008-08-28

Posts: 21

Permutations and combinations

On a math test a student is to select any four out of ten problems of equal difficulty. the test contains 2 geometry, 3 algebra, 1 statistics, and 4 probability problems.

How many different four-problems selections are possible if each selection includes the same number of algebra problems as probability problems?

All_Is_Number

Member

Registered: 2006-07-10

Posts: 258

Re: Permutations and combinations

We need to look at 2 different possible scenarios: 2 algebra and 2 probability, or 1 of each algebra and probability. (3 of each would exceed a total of four, and none of each would only leave 3 other questions.)

For 2 of each: nCr(3,2)*nCr(4,2)

For 1 each of algebra and probability, plus 2 from the others: nCr(3,1)*nCr(4,1)*nCr(3,2)

Add the results of the two scenarios to get your final answer.

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