Answer
30 times
Work Step by Step
Consider the equation for the condition at which the bus fare with discount pass is equal to the bus fare without discount
$1.25x=15+0.75x$
Here, x is the number of times in a month the bus must be used
Now, solve the above equation
$\begin{align}
& 1.25x=15+0.75x \\
& 1.25x-0.75x=15 \\
& 0.5x=15 \\
& x=30
\end{align}$
Thus, the number of times the bus must be used in a month is 30.
