A person has got 15 aquantances of which 10 are relatives. In how many ways he may invite 9 guests so that 7 would be relatives?
[I am a beginner so please explain the result]
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2 Answers
106we need to select 7 out of 10 relatives and 2 out of the remaining 5 acquaintances
selection of 7 relatives out of 10 can be done in: 10C7 ways = 10!/(7!3!) = 120 ways
similarly selection of 2 guests out of remaining 5 acquaintances can be done in 5C2 ways = 5!/(2!3!) = 10 ways
so total no. of ways = 120*10 = 1200 ways
1I know that but answer given 1380....how is it possible!!!??? is it printing mstake?