ACT Math · Probability and counting

In how many ways can a committee of 3 people be chosen from a group of 8 people?

In how many ways can a committee of 3 people be chosen from a group of 8 people?

Answer and explanation

Answer: G: 56

The order of selection does not matter for a committee, so use a combination: (83)=8!3! 5!=8⋅7⋅63⋅2⋅1=56\binom{8}{3}=\frac{8!}{3!\,5!}=\frac{8\cdot7\cdot6}{3\cdot2\cdot1}=56, choice G. Choice H (336336) is the permutation 8⋅7⋅68\cdot7\cdot6, which counts each group 3!=63!=6 times because it treats different orders of the same three people as different committees. Choice F (2424) is 8⋅38\cdot3, a product that does not model any selection. Choice J (512512) is 838^3, which would count ordered choices with repetition allowed, impossible for a committee of distinct people.

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