A pump started filling an empty pool with water and continued at a constant rate until the pool was full. At noon the pool was \(\dfrac13\) full, and \(1\frac14\) hours later it was \(\dfrac34\) full. What was the total number of hours that it took the pump to fill the pool?
A. \(2\frac13\)
B. \(2\frac23\)
C. \(3\)
D. \(3\frac12\)
E. \(3\frac23\)
Answer: C
Source: GMAT Prep
A pump started filling an empty pool with water and continued at a constant rate until the pool was full. At noon the po
This topic has expert replies

 Legendary Member
 Posts: 1552
 Joined: 01 Mar 2018
 Followed by:2 members
Timer
00:00
Your Answer
A
B
C
D
E
Global Stats
GMAT/MBA Expert
 [email protected]
 GMAT Instructor
 Posts: 15949
 Joined: 08 Dec 2008
 Location: Vancouver, BC
 Thanked: 5254 times
 Followed by:1267 members
 GMAT Score:770
For this type of question, I like to assign a "nice value" to the job.Gmat_mission wrote: ↑Sat Oct 31, 2020 6:24 amA pump started filling an empty pool with water and continued at a constant rate until the pool was full. At noon the pool was \(\dfrac13\) full, and \(1\frac14\) hours later it was \(\dfrac34\) full. What was the total number of hours that it took the pump to fill the pool?
A. \(2\frac13\)
B. \(2\frac23\)
C. \(3\)
D. \(3\frac12\)
E. \(3\frac23\)
Answer: C
Source: GMAT Prep
In this case we're looking for a number that works well with 1/3, 3/4 and even 1 1/4
So, let's say the pool has a capacity of 60 liters.
At noon the pool was 1/3 full, . . .
1/3 of 60 liters = 20 liters
So, at 12:00pm, the pool contained 20 liters of water
. . . and 1 1/4 hours later it was 3/4 full.
1 1/4 hours = 1.25 hours = 75 minutes.
3/4 of 60 liters = 45 liters
So, at 1:15pm, the pool contained 45 liters of water
What was the total number of hours that it took the pump to fill the pool?
45 liters  20 liters = 25 liters
So, in 1.25 hours, 25 liters of water was added to the pool
Rate = output/time
So, the rate at which water is added to the pool = (25 liters)/(1.25 hours) = 20 liters per hour
Time = output/rate
So, at a rate of 20 liters per hour, the time it takes to fill the 60 liter pool = 60/20 liters = 3 hours
Answer: C