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13 Feb 2011, 14:18
Kudos
Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
15%
(low)
Question Stats:
79% (00:50) correct
21%
(01:00)
wrong
based on 98
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Machine A can finish of a work in 4 hours, while В can finish of the work in 2 hours, and С can finish of the work in 8 hours. How many hours will it take for A, B, and С together to finish the work?
(A) 7/8 hours.
(B) 1 hour.
(C) 8/7 hours.
(D) 9/7 hours.
(E) 10/7 hours.
(A) 7/8 hours.
(B) 1 hour.
(C) 8/7 hours.
(D) 9/7 hours.
(E) 10/7 hours.
13 Feb 2011, 14:55
Kudos
Bookmarks
banksy
Machine A can finish of a work in 4 hours, while В can finish of the work in 2 hours, and С can finish of the work in 8 hours. How many hours will it take for A, B, and С together to finish the work?
(A)
(B)
(C)
(D)
(E)
(A)
(B)
(C)
(D)
(E)
General formula for multiple entities: \(\frac{1}{t_1}+\frac{1}{t_2}+\frac{1}{t_3}+...+\frac{1}{t_n}=\frac{1}{T}\), where \(T\) is time needed for these entities to complete a given job working simultaneously.
For example if:
Time needed for A to complete the job is A hours;
Time needed for B to complete the job is B hours;
Time needed for C to complete the job is C hours;
...
Time needed for N to complete the job is N hours;
Then: \(\frac{1}{A}+\frac{1}{B}+\frac{1}{C}+...+\frac{1}{N}=\frac{1}{T}\), where T is the time needed for A, B, C, ..., and N to complete the job working simultaneously.
Check this for more: word-translations-rates-work-104208.html#p812628
For our original question it'll be: 1/4+1/2+1/8=1/T --> 7/8=1/T --> T=8/7.
Answer: 8/7 hours.
Please provide answer choices for PS questions.
