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OG Quantitative Review #110

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OG Quantitative Review #110 [#permalink] New post 12 Feb 2008, 00:08
I still don't understand this problem - please help!

A certain clock marks every hour by striking a number of times equal to the hour, and the time required for a stroke is exactly equal to the time interview between strokes. At 6:00 the time lapse between the beginning of the first stroke and the end of the last stroke is 22 seconds. At 12:00, how many seconds elapse between the beginning of the first stroke and the end of the last stroke?

A) 72
B) 50
C) 48
D) 46
E) 44



Answer is D) 46. The explanation in the book reads, "At 6:00 there are 6 strokes and 5 intervals between strokes. <ok...I get this part> Thus, there are 11 equal time intervals in the 22 seconds between the beginning of the first stroke and the end of the last stroke. <huh? how did they get 11???> Therefore, each time interval is 22/11 = 2 seconds long. At 12:00 there are 12 strokes and 11 intervals between strokes. Thus, there are 23 equal 2-second intervals, or 23 x 2 = 46 seconds between the first and last stroke.

I am totally lost. Can someone please explain the logic behind this problem (in layman terms please)...? :wink:
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Re: OG Quantitative Review #110 [#permalink] New post 12 Feb 2008, 00:56
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6:00 BOOMS____BOOMS____BOOMS____BOOMS____BOOMS____BOOMS
6 booms
5 pauses
if t is duration of "booms", the total time for 6:00 is T(6)=6*t+5*t=11*t
T(6)=6*t+5*t=22
t=2 sec.

12:00 BOOMS____BOOMS____BOOMS____BOOMS____BOOMS____BOOMS____BOOMS____BOOMS____BOOMS____BOOMS____BOOMS____BOOMS
12 booms
11 pauses
the total time for 12:00 is T(12)=12*t+11*t=23*t=23*2=46

Hope this help :-D
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Re: OG Quantitative Review #110 [#permalink] New post 12 Feb 2008, 03:08
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they're only testing one concept. if there are x markings, then there will be x-1 intervals.

say there are 3 flags equally spaced on the ground. there are 2 intervals between those flags.

1 _ 2 _ 3
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Re: OG Quantitative Review #110 [#permalink] New post 13 Feb 2008, 01:16
hey thanks guys (or gals...for some reason i tend to think that all gmatclubbers are guys). your explanations really help! now if only i could think that logically during the exam...sigh. kudos for both of u! :)
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Re: OG Quantitative Review #110 [#permalink] New post 13 Feb 2008, 01:39
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lmshaw wrote:
hey thanks guys (or gals...for some reason i tend to think that all gmatclubbers are guys).


girls very rare ride on sport bikes, though I know some unique girls... :shock:
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Re: OG Quantitative Review #110 [#permalink] New post 13 Feb 2008, 09:31
When you get a question such as this and have no idea how to work it, you can narrow it down to 2 choices at least.

Try to figure out answer choices by just looking at problem and doing arith with the numbers. You know to eliminate them !!

Ok so it mentions 22 seconds, any multiple of 22 is out, so 44 is out.

then the time difference is 6 hours, once again, any multiple of 6, OUT

That leaves us to guess between 50 & 46.


Dont know how great this works but this is definitely my personal guessing strategy
Re: OG Quantitative Review #110   [#permalink] 13 Feb 2008, 09:31
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