MI3 wrote:Q. Lindsay can paint 1/x of a certain room in 20 minutes. What fraction of the same room can Joseph paint in 20 minutes if the two of them can paint the room in an hour, working together at their respective rates?
A. 1/3x
B. 3x/(x - 3)
C. (x - 3) / 3x
D. x / (x - 3)
E. (x - 3) / x
Ans - C[/spoiler]
Let job = 30 units, let x=5.
In 20 minutes, Lindsay produces (1/x)*30= (1/5)*30 = 6 units.
Thus, in 60 minutes, Lindsay produces 3*6 = 18 units.
Since the job is completed in an hour, work produced by Joseph = 30-18 = 12 units.
Thus, in 20 minutes -- 1/3 the time -- Joseph completes (1/3)*12 = 4 units.
Fraction of the job completed by Joseph in 20 minutes = 4/30 = 2/15. This is our target.
Now we plug x=5 into the answers to see which yields our target of 2/15.
Only answer choice C works:
(x-3)/3x = (5-3)/(3*5) = 2/15.
The correct answer is
C.
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
