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27 Oct 2011, 14:17
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
77% (01:45) correct
23%
(01:59)
wrong
based on 638
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Bob and Alice can finish a job together in 3 hours. If Bob can do the job by himself in 5 hours, what percent of the job does Alice do?
A) 10
B) 20
C) 40
D) 50
E) 60
A) 10
B) 20
C) 40
D) 50
E) 60
31 Jan 2016, 12:23
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Bookmarks
Hi All,
This prompt is a variation on a Work Formula question. It can actually be solved in a variety of ways - based on the information that we're given, here's a method that minimizes the number of calculations that you have to do:
We're told that Bob and Alice can finish a job together in 3 hours and that Bob can do the job by himself in 5 hours. We're asked what PERCENT of the job that Alice completes.
Since Bob can do the job in 5 hours, he completes 1/5 of the job per hour. We're told that he and Alice BOTH work for 3 hours, so Bob completes...
(3 hours)(1/5 of the job per hour) = 3/5 of the job = 60% of the job.
Since Bob completes 60% of the job, Alice must complete the other 40%.
Final Answer:
GMAT assassins aren't born, they're made,
Rich
This prompt is a variation on a Work Formula question. It can actually be solved in a variety of ways - based on the information that we're given, here's a method that minimizes the number of calculations that you have to do:
We're told that Bob and Alice can finish a job together in 3 hours and that Bob can do the job by himself in 5 hours. We're asked what PERCENT of the job that Alice completes.
Since Bob can do the job in 5 hours, he completes 1/5 of the job per hour. We're told that he and Alice BOTH work for 3 hours, so Bob completes...
(3 hours)(1/5 of the job per hour) = 3/5 of the job = 60% of the job.
Since Bob completes 60% of the job, Alice must complete the other 40%.
Final Answer:
GMAT assassins aren't born, they're made,
Rich
General Discussion
Schools: HEC '15 (A) HKUST '15 (I) Said (D) Booth '15 (D) CEIBS '15 (A) Cranfield '14 (A) Jones '15 INSEAD Jan '13 Melbourne '15 NUS '15 (WL)
GMAT 1: 630 Q47 V29
Posts: 19
27 Oct 2011, 17:56
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Lets supposat W is work Done and for moement we say that
W = 1 unit.
While working together --> W = Rate * Time = (1/A + 1/B)*3
...> 1 = 3 ( 1/A+1/B) --------- (1)
While only Bob is working , W = 1 = Rate of Bob & 5 .....> Rate of Bob = 1/B = 1/5 ---- (2)
Plugging 2 in (1) will give us Rate of Alice = 1/A = 2/15
Work Done by Alice = 2/15*3 = 2/5
% of workd done by Alice = 2/5*100 = 40% ---(C)
W = 1 unit.
While working together --> W = Rate * Time = (1/A + 1/B)*3
...> 1 = 3 ( 1/A+1/B) --------- (1)
While only Bob is working , W = 1 = Rate of Bob & 5 .....> Rate of Bob = 1/B = 1/5 ---- (2)
Plugging 2 in (1) will give us Rate of Alice = 1/A = 2/15
Work Done by Alice = 2/15*3 = 2/5
% of workd done by Alice = 2/5*100 = 40% ---(C)
Thank you. 
