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Bunuel
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Machine A can complete a job in 12 hours, and Machine B can do the 15 Jan 2024, 02:30
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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)!

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15% (low)

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88% (01:54) correct 12% (02:28) wrong based on 210 sessions

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Machine A can complete a job in 12 hours, and Machine B can do the same job at 1/5 of the rate of Machine A. If Machine A completes 3/4 of the job and then Machine B finishes the remaining portion, what is the total amount of time taken by Machine A and Machine B?

(A) 18 hours
(B) 20 hours
(C) 24 hours
(D) 28 hours
(E) 30 hours


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Machine A can do a job in 12 hours at a constant rate and Machine B can do the same job at a 1/5 constant rate of machine A. If machine A does 3/4 of the job and then machine B do the rest of the job, what is the total amount of hours done by machine A and machine B?
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C
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Machine A can complete a job in 12 hours, and Machine B can do the Updated on: 15 Jan 2024, 08:11
Originally posted by VivekSri on 15 Jan 2024, 03:32.
Last edited by VivekSri on 15 Jan 2024, 08:11, edited 1 time in total.
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Bunuel
Machine A can complete a job in 12 hours, and Machine B can do the same job at 1/5 of the rate of Machine A. If Machine A completes 3/4 of the job and then Machine B finishes the remaining portion, what is the total amount of time taken by Machine A and Machine B?

(A) 18 hours
(B) 20 hours
(C) 24 hours
(D) 28 hours
(E) 30 hours


Show Spoiler
Machine A can do a job in 12 hours at a constant rate and Machine B can do the same job at a 1/5 constant rate of machine A. If machine A does 3/4 of the job and then machine B do the rest of the job, what is the total amount of hours done by machine A and machine B?
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OA is C
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Abhishek009
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Machine A can complete a job in 12 hours, and Machine B can do the 15 Jan 2024, 08:03
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Bunuel
Machine A can complete a job in 12 hours, and Machine B can do the same job at 1/5 of the rate of Machine A. If Machine A completes 3/4 of the job and then Machine B finishes the remaining portion, what is the total amount of time taken by Machine A and Machine B?

(A) 18 hours
(B) 20 hours
(C) 24 hours
(D) 28 hours
(E) 30 hours
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Let total work be 60 units...

Efficiency of A is 5 units/hr, Efficiency of B is 1 unit/hour

Work completed by A is 3/4*60 = 45 Units, thus 15 units are left....

Time required by A to complete 45 units is 45/5 = 9 Hours...

Time required by B to complete 15 units is 15/1 = 15 Hours...

SO, Total Time taken is 9 +15 = 24, Answer must be (C)
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Machine A can complete a job in 12 hours, and Machine B can do the 15 Jan 2024, 15:01
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should be C ) use 1/time as rate and its easy then.
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Machine A can complete a job in 12 hours, and Machine B can do the 01 Feb 2024, 03:22
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I used the percent approach presented on the Tips and Hints post (https://gmatclub.com/forum/tips-and-hin ... 72096.html)
We assume that the task is 100%
A does 100% of the job in 12 hours (100/12). So A will take x hours to complete 3/4 (75%) of the job -- 100x = 12*75; x = 900/100; x = 9 hours
B does 100% of the job at 1/5 of the rate of A. This means, machine B es SLOWER than machine A.
Use the reciprocal to understand machines B work rate -- 5/1 of 12 = 60 hours. Hence machine B does 100% of the job in 60 hours (100/60).
How many minutes does machine B take to complete the remaining 25% of the job (100%-75% already completed by machine A)?
100x = 25*60; x = 1500/100; x= 15

Now we add 15+9 = 24

Hope it helps!
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Machine A can complete a job in 12 hours, and Machine B can do the 27 Sep 2025, 05:16
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