Please verify this word problem for me!

[krisolaw]

Filling a pool. One inlet pipe can fill an empty pool in 4 hours, and a drain can empty the pool in 8 hours. How long will it take the pipe to fill the pool if the drain is left open?

1/4 - 1/8 = 1/x

2x - x = 8
x = 8
therefore it will take 8 hours to fill the pool.

Thanks!

 

[tkhunny]

I guess...

I don't like this problem. The drain most certainly does not drain at a constant rate, particularly not at the very beginning.

Whatever...

I think you have done the problem as intended.

 

[elchichita]

I guess...

I don't like this problem. The drain most certainly does not drain at a constant rate, particularly not at the very beginning.

Whatever...

I think you have done the problem as intended.

True! A problem like this should be approached with differential equations to get the correct answer...