Aman verma wrote:Q: A swimming pool is connected with four pipes A,B,C,D of which two can fill the pool and the other two can empty it. The time taken by A,B,C,D to finish their jobs are 10 hr, 15 hr, 20 hr and 30 hr respectively. All four pipes are opened when the pool was empty. It took 12 hrs to fill it completely. Which two are the outlet pipes ?
a) A & B
b) c & D
c) A & C
d) B & D
e) B & C
Let the pool = 60 units.
Rate for A = w/t = 60/10 = 6 units per hour.
Rate for B = w/t = 60/15 = 4 units per hour.
Rate for C = w/t = 60/20 = 3 units per hour.
Rate for D = w/t = 60/30 = 2 units per hour.
Two of these rates must serve to FILL the pool, implying two POSITIVE RATES.
The other two rates must serve to EMPTY the pool, implying two NEGATIVE RATES.
When the four rates are combined, the time to fill the pool must be 12 hours, implying the following COMBINED RATE:
w/t = 60/12 = 5 units per hour.
Only one combination works:
A + B - C - D = 6 + 4 - 3 - 2 = 5 units per hour.
Thus, A and B must be filling the pool, while C and D serve as OUTLET pipes emptying the pool.
The correct answer is
B.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at
[email protected].
Student Review #1
Student Review #2
Student Review #3
