A lady gives a dinner party to 5 guests to be selected from 9 friends. The number of ways of forming the party of 5 given that two of the friends will not attend the party together is
A
56
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B
126
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C
91
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D
None of these
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Solution
The correct option is C 91
There are 9 friends
If two of term do not attend the party together
Total no. of ways is select 5 from =7C5
=21 ways
If one of them is selected for party, then no. of ways=2C1×7C4=70 ways