A committee of 3 is to be formed from a group of 2 boys and 2...

Number of ways of selecting 2 boys out of 2 boys $={ }^2 C_2=1$. Number of ways of selecting 1 girl out of 2 girls $={ }^2 C_1=2$. Number of ways of selecting 3 out of 4 persons $={ }^4 C_3=4$. $\therefore$ Required probability $=\frac{{ }^2 C_1 \times{ }^2 C_2}{{ }^4 C_3}=\frac{2 \times 1}{4}=\frac{1}{2}$.