Working alone, printers X, Y, and Z can do a certain printing job, consisting of a large number of pages, in 12, 15, and 18 hours respectively. What is the ratio of the tme it takes printer X to do the job working alone at its raste, to the time it takes printers Y and Z to do the job, working together at their individual rates?
A. 4/11
B. 1/2
C. 15/22
D. 22/15
E. 11/4
The OA is D, but I don't understand how. When I solved the problem I set up my equation as:
1/12 / [1/15 + 1/18] = 15/22...so why wouldn't the answer be C???
please help!
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Hi Nisha,
The Q asks us to find ratio of time take and not rate, in your explanation you have taken ratios of their rates thats why u got the reciprocal of the ans
now time for machine x is 12 hrs
y & z combined i.e combine their rates so we have 1/15 +1/18
i.e 33/15X18
i.e 11/90
we know that R X t =w
hence combined time of y & z is 1/(11/90) i.e 90/11
so our ratio is 12/90/11 i.e 12X11/90
i.e 22/15
In such q's you can always double check the numerator & denominator of the fraction you get as the answer& ask your self a question that which one should be bigger.
The Q asks us to find ratio of time take and not rate, in your explanation you have taken ratios of their rates thats why u got the reciprocal of the ans
now time for machine x is 12 hrs
y & z combined i.e combine their rates so we have 1/15 +1/18
i.e 33/15X18
i.e 11/90
we know that R X t =w
hence combined time of y & z is 1/(11/90) i.e 90/11
so our ratio is 12/90/11 i.e 12X11/90
i.e 22/15
In such q's you can always double check the numerator & denominator of the fraction you get as the answer& ask your self a question that which one should be bigger.
Regards
Samir
Samir