1.

From 8 gentlemen and 5 ladies, a committee of 4 is to be formed. In how many ways can this be done. (a) when the committee consists of exactly three gentlemen? (b) when the committee consists of at most three gentlemen?

Answer» (a) We have to select three out of 8 gentlemen and one out of 5 ladies. Hence, the number of ways in which this can be done `=.^(8)C_(3)xx.^(5)C_(1)=280`
(b) The committee is to contain at most three gentlemen, i.e., it may contain either 1,2 or 3 gentlemen.
Hence, the total number of ways `=.^(8)C_(1)xx.^(5)C_(3)+.^(8)C_(2)xx.^(5)C_(2)+.^(8)C_(3)xx.^(5)C_(1)=80+280+280=640`.


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