Answer
P(placebo) $=\frac{2}{5}=0.4$
Work Step by Step
The sample space: $150+100=250$ women in the study. So, N(S) = 250.
100 women received a placebo. So, N(placebo) = 100.
P(placebo) = $\frac{N(placebo)}{N(S)}=\frac{100}{250}=\frac{2}{5}=0.4$
