Can't seem to figure this one out....
Each of 10 machines works at the same constant rate doing a certain job. The amount of the time needed by the 10 machines working together, to complete the job is 16 hours. How many hours would be needed if only 8 of the machines, working together, were used to complete the job?
A. 18
B. 20
C. 22
D. 24
E. 26
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Combined Work Problem
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Brent@GMATPrepNow
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The amount of the time needed by the 10 machines working together, to complete the job is 16 hours.JScherman wrote:.
Each of 10 machines works at the same constant rate doing a certain job. The amount of the time needed by the 10 machines working together, to complete the job is 16 hours. How many hours would be needed if only 8 of the machines, working together, were used to complete the job?
A. 18
B. 20
C. 22
D. 24
E. 26
So, we can say that the job requires a total of 160 MACHINE HOURS (10 machines each working 16 hours = 160 machine hours)
How many hours would be needed if only 8 of the machines, working together, were used to complete the job?
We need to divide the work of 160 machine hours among the 8 machines.
160/8 = 20 hours
Answer: B
Cheers,
Brent
Here's a similar question to try: https://www.beatthegmat.com/work-problem-t275195.html
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PLUG IN approach:JScherman wrote:Can't seem to figure this one out....
Each of 10 machines works at the same constant rate doing a certain job. The amount of the time needed by the 10 machines working together, to complete the job is 16 hours. How many hours would be needed if only 8 of the machines, working together, were used to complete the job?
A. 18
B. 20
C. 22
D. 24
E. 26
Let the rate per machine = 1 unit per hour.
Rate for 10 machines = 10 units per hour.
In 16 hours, the amount of work produced by 10 machines = r*t = 10*16 = 160 units.
To produce 160 units, the time required by 8 machines = w/t = 160/8 = 20 hours.
The correct answer is B.
INVERSE PROPORTION approach:
The number of machines and the number of hours are INVERSELY PROPORTIONAL.
As the number of machines DECREASES, the number of hours must INCREASE, so that the same amount of work is produced in each case.
Thus, we can set up the following equation:
(number of machines)(number of hours) = (number of machines)(number of hours)
Since 10 machines require 16 hours, and we must determine how many hours will be required by 8 machines, we get:
10*16 = 8x
x = 20.
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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].
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