An empty pool being filled with water at a constant rate

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BTGmoderatorRO: Moderator; Posts: 772; Joined: Wed Aug 30, 2017 6:29 pmFollowed by: 6 members

by BTGmoderatorRO » Thu Mar 01, 2018 12:34 pm

An empty pool being filled with water at a constant rate takes 8 hours to fill to 3/5 of its capacity. How much more time will it take to finish filling the pool?

(A) 5 hr 30 min
(B) 5 hr 20 min
(C) 4 hr 48 min
(D) 3 hr 12 min
(E) 2 hr 40 min
OA is B

what is the best mathematical approach to use here? please i need help from expert here
Thanks<i class="em em-blush"></i>

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Source: Beat The GMAT — Problem Solving | Thu Mar 01, 2018 12:34 pm

mbawisdom: Senior | Next Rank: 100 Posts; Posts: 94; Joined: Tue Dec 16, 2014 9:50 amFollowed by: 4 members; Location: London, UK; Thanked: 2 times; GMAT Score:770

by mbawisdom » Mon Mar 05, 2018 8:08 am

Roland2rule wrote:An empty pool being filled with water at a constant rate takes 8 hours to fill to 3/5 of its capacity. How much more time will it take to finish filling the pool?

(A) 5 hr 30 min
(B) 5 hr 20 min
(C) 4 hr 48 min
(D) 3 hr 12 min
(E) 2 hr 40 min
OA is B

what is the best mathematical approach to use here? please i need help from expert here
Thanks<i class="em em-blush"></i>

Rate = Work/Time
R = (3/5)/8 = 3/40 pool per hour

We need to fill 2/5 of the pool to finish the job

3/40 = (2/5)/T
3/40 = (16/40)T
T = 16/3 = 5 1/3 hrs or 5 hrs and 20 min

Answer is (B) 5 hr 20 min

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Mon Mar 05, 2018 8:28 am

Roland2rule wrote:An empty pool being filled with water at a constant rate takes 8 hours to fill to 3/5 of its capacity. How much more time will it take to finish filling the pool?

(A) 5 hr 30 min
(B) 5 hr 20 min
(C) 4 hr 48 min
(D) 3 hr 12 min
(E) 2 hr 40 min

Here's another approach:

IMPORTANT CONCEPT: After 8 hours, 3/5 of the job is finished and 2/5 of the job is remaining.
This means the remaining part of the job is 2/3 the size of the first part of the job.
Think of it this way:
If the pool had a capacity of 5 gallons, then the first part of the job would be filling 3 gallons, and the remaining part of the job is filling 2 gallons.
So, the remaining part of the job (filling 2 gallons) is 2/3 the size of the first part of the job (filling 3 gallons)

So, if it takes 8 hours to do the first part of the job, the time to do the remaining part = 2/3 of 8 hours
2/3 of 8 hours = 2/3 x 8 hours
= 16/3 hours
= 5 1/3 hours
= 5 hours 20 minutes

Answer: B

Brent Hanneson - Creator of GMATPrepNow.com

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by [email protected] » Mon Mar 05, 2018 8:43 pm

Hi Roland2rule,

We're told that 8 hours fills 3/5 of the pool; the question asks how long it will take to fill the remaining 2/5 of the pool. Since the pool is filling at a constant rate, we can use a ratio to answer the question. The ratio can be written in a number of different ways; I used the following ratio:

8/X = (3/5)/(2/5)

Simplifying, we get...

8/X = 3/2

Now, cross-multiply...

3X = 16

X = 5 1/3 hours

Final Answer: B

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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swerve: Legendary Member; Posts: 2535; Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

by swerve » Tue Mar 06, 2018 8:13 am

Hi,

As the pool is filled at a constant rate, you can solve it as follow,

8 hours....................................................... 3/5
X hours....................................................... 2/5

Then,
$$X=\frac{8\cdot\frac{2}{5}}{\frac{3}{5}}=\frac{16}{3}=5.33\ hours$$
X = 5 hours and 20 minutes. Option B.

Regards!

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8137; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Tue Mar 06, 2018 9:23 am

Roland2rule wrote:An empty pool being filled with water at a constant rate takes 8 hours to fill to 3/5 of its capacity. How much more time will it take to finish filling the pool?

(A) 5 hr 30 min
(B) 5 hr 20 min
(C) 4 hr 48 min
(D) 3 hr 12 min
(E) 2 hr 40 min

We can let n = the time it takes to fill the remaining 2/5 of the pool and create the proportion:

8/(3/5) = n/(2/5)

40/3 = 5n/2

80 = 15n

n = 80/15 = 16/3 = 5 1/3 hours = 5 hours and 20 minutes

Answer: B

Scott Woodbury-Stewart
Founder and CEO
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

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