Two interior angles of a convex pentagon are right angles and the other three interior angles are congruent. In degrees, what is the measure of one of the three congruent interior angles?
The sum of the interior angles of a polygon with $n$ sides is $180(n-2)$. The pentagon has 5 sides, so the sum of the interior angles is $180\cdot3$. We subtract the degree measures of the two right angles to get $180\cdot3-90-90=180\cdot2$, which is the sum of the measures of the three congruent interior angles. We divide by 3 to get the measure of one of the three congruent interior angles: $\frac{180\cdot2}{3}=60\cdot2=\boxed{120^\circ}$.