two pipes filling a pool. how many hours does it take?

Question

A pool can be filled by one pipe in 6 hours and by a second pipe in 8 hours. How long will it take using both pipes to fill the pool

Answer 1

Katelyn, this is easier than it seems, I promise!

 

In one hour, pipe 1 fills 1/6 of the pool, and pipe 2 fills 1/8 of the pool. Let x be the time it takes both pipes to fill the pool.

 

We then say (1/6)x + (1/8)x = 1

 

The LCM of 6 and 8 is 24, so we have (4/24)x + (3/24)x = 1

 

So, (7/24)x = 1

 

We divide both sides by 7/24 and get x = 24/7, or 3.43 hours, or about 3 hours and 26 minutes.

 

Hope this helps!