Question
A person has got 15 acquaintances of whom 10 are relatives. In how many ways, may he invite 9 guests so that 7 of them would be relatives?
Step 1
He wants to invite 9 guests such that 7 of them are relatives. So, we need to select 7 relatives out of 10. This can be done in ${10 \choose 7}$ ways. Show more…
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