Question

A pool can be filled by one pipe in 6 hours and by a second in 12 hours . How long will it take using both pipes to fill the pool?

Answer 1

4 hours

Explanation:

Part of the pool filled by first pipe in an hour = 1/6

Part of the pool filled by second pipe in an hour = 1/12

Part of the pool filled by first pipe and second pipe in an hour = 1/6 +1/12

`=(1*2)/(6*2)+(1)/(12)\\= (2)/(12)+(1)/(12)\\\\=(3)/(12)\\\\=(1)/(4)`

Time taken by both the pipes to fill the pool = 4 hours

Answer 2

One pipe = 1/6 of the pool in one hour
Second pipe = 1/12 of the pool in one hour
Let x be the time
Make them equal to 1 (total of pool)
1/6(x) + 1/12(x) = 1
Make non fraction by multiplying by 12
2x + 1x = 12
3x = 12, x = 4
It would take 4 hours