Answer:
The least amount of time (in hours) both pumps need to be open is 3 hours.
Step-by-step explanation:
According to the Question,
Let the Capacity of the Pool is 36Litre.
If the pool needs to be filled in 10 hours the least amount of time (in hours) both pumps need to be open is 3 hours.
Note:- if 3 hour both pipe open so 3 x (5) = 15 ltr Pool is Filled.
Now For Remaining 7 hour Pipe A with Efficiency 3 ltr/hour is open alone to fill the pool Remaining 7 x 3 = 21 ltr . Total 21+15 = 36ltr .