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
