Answer
$\dfrac{7}{8}$ or $87.5\%$
Work Step by Step
Use the formula for mutually exclusive events to find the probability of the events not happening at the same time.
The formula is $P(C$ $or$ $D)=P(C)$ $+$ $P(D)$.
We are given $P(C)=\dfrac{1}{2}$ and $P(D)=\dfrac{3}{8}$.
Plug the values into the formula:
$P(C$ $or$ $D)$ = $\dfrac{1}{2}$ $+$ $\dfrac{3}{8}$
$P(C$ $or$ $D)$ = $\dfrac{4}{8}+\dfrac{3}{8}$
$P(C$ $or$ $D)$ = $\dfrac{7}{8}$
$P(C$ $or$ $D)$ $=87.5\%$
