Answer
$1$ or $100$%
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 $P(C$ $or$ $D)=P(C)$ $+$ $P(D)$.
$P(C)$ is $\dfrac{2}{5}$ and $P(D)$ is $\dfrac{3}{5}$.
Plug the values into the formula:
$P(C$ $or$ $D)$ = $\dfrac{2}{5}$ $+$ $\dfrac{3}{5}$
$P(C$ $or$ $D)$ = $\dfrac{5}{5}$
$P(C$ $or$ $D)$ $=1=100$%
