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Number of hours

by Brent@GMATPrepNow » Thu Dec 18, 2008 9:01 pm
If a certain machine begins operating at x:00 a.m. on Wednesday and runs continuously until y:00 p.m. the following day (Thursday), how many hours did the machine operate?
A) x + y + 18
B) x + y + 24
C) 2x - y + 24
D) y - x + 36
E) 48 - x - y

Answer: D
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by brb588 » Thu Dec 18, 2008 9:31 pm
I know this may not be the most elegant way, but the quickest way for me was to pick numbers. I computed in my head that if the machine started at 3 AM Wed. and ended 5 PM Thurs., it worked 38 hours.

A. 3 + 5 + 18 ≠ 38
B. 3 + 5 + 24 ≠ 38
C. 2(3) - 5 + 24 ≠ 38
D. 5 - 3 + 36 = 38

And just to make sure...

E. 48 - 3 - 5 ≠ 38

It's D.
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by vishubn » Thu Dec 18, 2008 9:35 pm
if machine started working in midnight... that is
1 am
x=1:00am

and it worked till 1:00 pm that is 36hrs

it worked 12 hrs

pluggin in back

x=1
y=1

D)y-x+36== is the OA
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by Brent@GMATPrepNow » Thu Dec 18, 2008 9:37 pm
Hmmm, I'll have to change my distractors :)
I figured that some people might plug in something like 9:00 am to 5:00 pm, and for those people, A (x+y+18) would have worked.
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by raunekk » Thu Dec 18, 2008 9:38 pm
imo:D

1st) its X AM.- Thus starting from 0:0 hours in the morning we have X hours passed

Thus no of hours wednesday will be= 24-x...(1)

now 2nd) its Y PM - The number Y will state the sumber of hours after noon i.e 12 PM

Thus the total number of hours on thursday = 12+y..(2)

adding 1 and 2 = y-x+36
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