52. One fountain fills the pool in 2.5 hours, the other in 3.75 hours. How long will it take for both fountains to fill the pool?
52. If both fountains together fill the pool in $x$ hours, then, considering that the first fountain fills $\frac{2}{5}$ of the pool per hour, and the second fills $\frac{4}{15}$ of the pool per hour, we get the equation: $\frac{2}{5}+\frac{4}{15}=\frac{1}{x}$, from which $x=1.5$. Answer: in 1.5 hours.