Friends and relatives.
Probability
Level
3
A person has 12 friends, including 8 relatives. In how many ways he can invite 7 friends, including 5 relatives?
The answer is 336.
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1 solution
He must invite 5 relatives and 2 non-relatives.
The number of ways of doing this is ( 5 8 ) ( 2 4 ) = 5 6 ∗ 6 = 3 3 6