please help me with this problem

Question

A swimming pool holds 600,000 liters of water. The pool has two drainage pipes. When the pool is completely full, the first pipe alone can empty it in 150 minutes, and the second pipe alone can empty it in 100  minutes. When both pipes are draining together, how long does it take them to empty the pool?

Answer 1

Each minute, the first pipe empties 1/150th of the pool and the second pipe empties 1/100th of the pool.

Let x be the amount of time (in minutes) that it takes to empty the pool if both pipes are used.

Then 1/150 + 1/100 = 1/x

100x + 150x = 15000

250x = 15000

x = 60 minutes

Answer 2

The first pipe drains at a rate of 600,000 liters in 150 minutes or 4000 liters/minute.

The second pipe drains at a rate of 600,000 liters in 100 minutes or 6000 liter/minute.

So if both pipes are open, the rate will be 4000 + 6000 or 10,000 liters/minute.

(600,000 liters)/(10,000 liters/min) = 60 minutes.