SOLUTION: How many ways can a 3-people committee be chosen from 10 twins(20 people)? Restriction: No twins can both exist in this committee. (e.g Assume A & B are twins, if A is in the commi

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Question 548939: How many ways can a 3-people committee be chosen from 10 twins(20 people)? Restriction: No twins can both exist in this committee. (e.g Assume A & B are twins, if A is in the committee, B cannot be in.)
Found 2 solutions by josmiceli, Macy101:
Answer by josmiceli(19441) (Show Source):
You can put this solution on YOUR website!
The 1st choice is any one of 20
---------
There are 19 left, but one of them is
the twin of the 1st choice, so there
are 18 valid 2nd choices
---------
There are 17 3rd choices, but one of these is
the twin of the 2nd choice, so there are
16 valid 3rd choices

Answer by Macy101(1) (Show Source):
You can put this solution on YOUR website!
I believe this could be a wrong answer�
You're certain that 2 persons that are twins can NEVER be in the committee together. So actually, you can look at it as if those twins count as 1 person right?
So this leaves us to choose 3 persons out of 10.

10!/( 3! * (10 - 3)!) = 120