Question

A certain pipe can be used to fill a pool with water in 2 hours. A second pipe can be used to fill the pool in 4 hours. How long does it take to fill the pool when both pipes are used at the same time?​

Answer 1

Answer:

1 1/3 hours

Step-by-step explanation:

Pipe 1 alone:

fills the pool in 2 hours

in 1 hour, it fills 1/2 of the pool

Pipe 2 alone:

fills the pool in 4 hours

in 1 hour, it fills 1/4 of the pool

Pipe 1 and Pipe 2 working together:

fill the pool in x hours

in 1 hour, they fill 1/x of the pool

Working together, in 1 hour the two pipes fill 1/2 + 1/4 of the pool.

Working together, in 1 hour the two pipes fill 1/x of the pool.

Therefore,

1/2 + 1/4 = 1/x

2/4 + 1/4 = 1/x

3/4 = 1/x

x = 4/3

x = 1 1/3

Answer: 1 1/3 hours