Answer
$\dfrac{3}{4}$ or $75\%$
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 $P(S$ $or$ $T)=P(S)$ $+$ $P(T)$.
We have $P(S)=\dfrac{5}{8}$ and $P(T)=\dfrac{1}{8}$.
Plug the values into the formula:
$P(S$ $or$ $T)$ = $\dfrac{5}{8}$ $+$ $\dfrac{1}{8}$
$P(S$ $or$ $T)$ = $\dfrac{6}{8}$
$P(S$ $or$ $T)$ = $\dfrac{3}{4}=75\%$
