Answer
P(placebo or headache went away within 45 minutes) $=\frac{116}{125}=0.928$
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.
There were a total of $132+56=188$ women whose headache went away within 45 minutes. So, N(headache went away within 45 minutes) = 188.
According to the cell in the second row, first column: N(placebo and headache went away within 45 minutes) = 56.
P(placebo or headache went away within 45 minutes) = P(placebo) + P(headache went away within 45 minutes) - P(placebo and headache went away within 45 minutes) =
$\frac{N(placebo)}{N(S)}+\frac{N(\text{headache went away within 45 minutes})}{N(S)}-\frac{N(\text{placebo and headache went away within 45 minutes})}{N(S)}=\frac{100}{250}+\frac{188}{250}-\frac{56}{250}=\frac{232}{250}=\frac{116}{125}=0.928$
