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Intern
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Clock [#permalink] New post 02 Nov 2010, 23:29
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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 interval 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
[Reveal] Spoiler: OA
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Re: Clock [#permalink] New post 02 Nov 2010, 23:33
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At 6:00 it'll chime 6 times. If we assume that the time taken to chime is x, then time between chimes is also x. So you have 6 chimes, which is 6x and 5 time intervals between chimes. This means that 11x = 22 seconds. Thus x = 2 seconds.

By a similar logic, at 12:00, there are 12 chimes and 11 intervals so the total time is (12+11)x = 23x = 46 seconds.

Is the answer right? Please post the OA.

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Re: Clock [#permalink] New post 02 Nov 2010, 23:40
student26 wrote:
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 interval 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


At 6:00, there are 6 strokes :
Strke<-->Strke<-->Strke<-->Strke<-->Strke<-->Strke
This last 22 seconds
There 6 strokes and 5 intervals, each of which lasts 2 seconds (22/11)

At 12:00 :
Strke<-->Strke<-->Strke<-->Strke<-->Strke<-->Strke<-->Strke<-->Strke<-->Strke<-->Strke<-->Strke<-->Strke

Which is exactly 2x(time taken for 6:00)+1 extra interval
This 2x22+2 = 46 seconds

Answer : (d)
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Re: Clock [#permalink] New post 09 Nov 2010, 05:52
Notice 2 things-
1. stroke time == interval time
2. Beginning of first stroke to end of last stroke indicates 1 interval time lesser than number of strokes.

For 6 'o clock--> strokes =6 and intervals=5, which take 22 seconds i.e. 2 sec per stroke/interval
for 12 'o clock-> strokes=12 and intervals=11, total 23 so the time interval=46

Answer:-D
Re: Clock   [#permalink] 09 Nov 2010, 05:52
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