You can fill the pool using two different water sources. The first source fills it completely in 30 minutes by itself and the second source fills it completely in 90 minutes by itself. How many minutes will it take to fill the pool with both sources working together?
+36915 1/30 + 1/90 = 1/x solve for 'x' the amount of time required for both working together
3 / 90 + 1/90 = 1/x
4/90 = 1/x
90/4 = 22.5 minutes = x
