Question

The probability that a kid is not a swimmer is $\frac{1}{5}$. Then the probability that out of the five kids, four are swimmers is:

• A.
• B.
• C.
• D. None of these

Answer 1

The correct option is B

4 kids out of 5 can be selected in ${}^5{C}_4$ways.
Probability of a kid being not a swimmer = $\frac{1}{5}$
Probability of a kid being a swimmer = (1-$\frac{1}{5}$) = $\frac{4}{5}$
Required probability = ${}^5{C}_4$$\times$($\frac{1}{5}$)$\times$${\left(\frac{4}{5}\right)}^4$