flower07 wrote:

One pipe can fill a pool 1.25 times faster than a second pipe. When both pipes are opened, they fill the pool in five hours. How long would it take to fill the pool if only the slower pipe is used?

A. 11.25

B. 11.52

C. 1.25

D. 9

E. 7.2

I would appreciate if someone can explain me this using the Rate Time Work chart (as used by Manhattan). That will help me understand better and easier.

Thank you!

Let me give you an elaborate explanation on how you can use this (I have also used MGMAT's way of approaching the problems, but adopted according to the time needs)

Let's assume the rate of the slower pipe is: x

So, the rate of the faster pipe would be: 1.25x

Working together, their rate will be x + 1.25x = 2.25x

As the question says, they take 5 hours to fill up the tank working together, so:

Rate x Time = Work

2.25x x 5 = 1

2.25x = 1/5

x = 1/5 / 2.25 = 4/45

So, the rate of the slower pipe, x = 4/45

Now, let's see how long it takes for the slower pipe to complete the task:

Rate x Time = Work

4/45 x Time = 1

Time = 1 / 4/45 = 45/4 = 11.25

Hope it's clear