Chapter 12 - Counting and Probability - Section 12.3 Probability - 12.3 Assess Your Understanding - Page 885: 40

$\dfrac{3}{8}$ or $0.375$

We know that probability$=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}.$ The possible outcomes: $\{BBBB,GBBB,BGBB,BBGB,BBBG,GGBB,GBGB,GBBG,BGGB,BGBG,BBGG,BGGG,GBGG,GGBG,GGGB,GGGG\}$ Hence, here because there are $6$ possible outcomes with $2$ girls and $2$ boys and $16$ outcomes in total, $P(\text{$2$ girls and $2$ boys })=\frac{6}{16}=\frac{3}{8}=0.375$