Chapter 13 - Counting and Probability - 13.3 Probability - 13.3 Asses Your Understanding - Page 865: 40

$0.375.$

The possible outcomes are: $GGGG,GGGB,GGBG,GBGG,BGGG,BBGG,BGBG,GGBB,GBGB,GBBG,BGGB,GBBB,BGBB,BBGB,BBBG,BBBB$, which is $16$ outcomes, and $6$ are good outcomes (and all are equally likely). We know that probability$=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}.$ Hence here probability$=\frac{6}{16}=0.375.$