Question

a swimming pool holds 585,000 liters of water. the pool has two drainage pipes. when the pool is completely full, the first pipe alone can empty it in 195 minutes, and the second pipe alone can empty it in 130 minutes. when both pipes are draining together, how long does it take them to empty the pool?
□ minutes

Explanation:

Step1: Find rate of first pipe

The first pipe empties 585000 liters in 195 minutes, so its rate is $\frac{585000}{195} = 3000$ liters per minute.

Step2: Find rate of second pipe

The second pipe empties 585000 liters in 130 minutes, so its rate is $\frac{585000}{130} = 4500$ liters per minute.

Step3: Find combined rate

Combined rate of both pipes is $3000 + 4500 = 7500$ liters per minute.

Step4: Find time to empty together

Time = Total volume / Combined rate = $\frac{585000}{7500} = 78$ minutes.

Answer:

78