Question

In a second grade class containing 12 girls and 11 boys, 2 students are selected at random to give out the math papers. what is the probability that both are girls?

Answer 1

The probability is defined as $\frac{number OfFavourableEvents}{numberOfEvents In TheSampleSpace}$.

The number of ways of selecting 2 girls from 12 girls is $C(2,12)=\frac{12!}{10!2!} =66$.The number of ways of selecting 2 student from $12+11=23$ students is $C(2,23)=\frac{23!}{21!2!} =253$.

The required probability is $\frac{66}{253} =\frac{6}{23} =0.261$