A person has 12 friends and he wants to invite 8 of them to a birthday party. Find how many times 3 particular friends will always attend the parties. Choose one: A) 126 B) 95 C) 130 D) 155 E) None
Explanation :   No. of times 3 particular friends will attend the party always.   Hence the number of ways of selection is :-   =&gt; n-kCr-k, where n= 12, r=8 and k=3.   =&gt; No. of combinations = 12-3C8-3 .   =&gt; 9C5.   =&gt; 126.   Hence, the number of combinations with 3 particular friends present in each combination (party) is 126.   126nswer : 126
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A person has 12 friends and he wants to invite 8 of them to a birthday party. Find how many times 3 particular friends will always attend the parties.