Question

A swimming pool can be filled by pipe A in 3 hours and by pipe B in 6 hours, each pump working on its own. At 9 am, pump A is started. At what time will the swimming pool be filled if pump B is started at 10 am?

• A. 11:20 a.m.
• B. 11:05 a.m.
• C. 11:10 a.m.
• D. 10:50 a.m.

Answer 1

The Correct Option is A

To determine when the pool will be filled, we need to calculate the filling rates of pumps A and B. Pipe A can fill the pool in 3 hours, and pipe B can fill it in 6 hours.

We will calculate how much of the pool each pipe fills per hour: 

• Pipe A's rate is 13 of the pool per hour.
• Pipe B's rate is 16 of the pool per hour.

From 9 am to 10 am, only pipe A is working, so in 1 hour:

• Pipe A fills 13 of the pool.

At 10 am, pipe B is also started, so both pipes work together from 10 am onward. Their combined rate is:

• Combined rate = 13 + 16 = 12 of the pool per hour.

The amount of the pool left to fill at 10 am is:

1-131=23.

Now calculate the time it will take to fill 23 of the pool with both pipes working together:

23÷12=23×2=43 hours.

43 hours is split into full hours and remaining minutes; it is 1 13 hours, which amounts to 1 hour and 20 minutes.

This means the pool will be completely filled at:

• 10 am + 1 hour and 20 minutes = 11:20 am.

Therefore, the swimming pool will be filled at 11:20 a.m.