Source: Official Guide for the GMAT 13th Ed. Problem Solving; #168 Official Guide for the GMAT 2015 14th Ed. Problem Solving; #168

1

An empty pool being filled with water

An empty pool being filled with water at a constant rate takes hours to fill 3/5 of its capacity. How much more time will it take to finish filling the pool?

1 Explanation

2

Gravatar Mike McGarry, Magoosh Tutor

Dec 28, 2013 • Comment

Leah Williams

For this question could you do 3/5 *8= 24/5

24/5=4.8= 5hr. 20m

Feb 5, 2016 • Reply

Cydney Seigerman, Magoosh Tutor

Hi Leah :)

I'm not sure how you determine 4.8 = 5h20m

Let's look at the first step of your solution, keeping in mind the units of the quantities:

3/5 pools * 8 h = 24/5 pools*h

At this point, we have a unit that doesn't really help us in the question. We need to figure out how long it takes to fill up 2/5 of the pool, which we could write in the form

x hr / (2/5 pools)

As you can see, here, we're dividing the terms, not multiplying them. And to be able to use the information given in the problem, we need to put it in this form. For example:

8 hr / (3/5 pools) = 13 1/3 hr/pool

And now, we can solve for x above:

x hr / (2/5 pools ) = 13 1/3 hr / pools
x hr = (13 1/3 hr)*(2/5 pools)/ pools
x hr = 5 1/3 hr = 5 hr 20 min

I hope this helps :)

Feb 6, 2016 • Reply

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