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# A certain clock marks every hour by striking a number of times equal

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Senior Manager
Joined: 17 Aug 2018
Posts: 387
Location: United States
GMAT 1: 610 Q43 V31
GMAT 2: 640 Q45 V32
GMAT 3: 640 Q47 V31
GRE 1: Q155 V155
WE: General Management (Other)
Re: A certain clock marks every hour by striking a number of times equal  [#permalink]

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15 Jul 2019, 07:08
Perfect question to pick your favorite answer choice and move on at the exam lol.
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Joined: 05 Feb 2018
Posts: 440
Re: A certain clock marks every hour by striking a number of times equal  [#permalink]

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13 Aug 2019, 10:43
Bunuel 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

We are given time stroke = time between strokes, the trap here is to assume they are equivalent and get messed up in calculating those numbers. However, it's stated that we are counting the "time between the first and last stroke" only; i.e. there is no interval on the last stroke.

This is a good question to draw a diagram:

x = stroke, o = interval

x-o-x-o-x-o-x-o-x-o-x
1---2---3---4---5----6

You can see there are 6 x's and only 5 o's, this means 22 secs is evenly divided by 11... 2 secs per stroke
Now, applying the same logic to 12, it would be double the number of strokes (24) minus 1 (for the cut-off at the end).

2*23 = 46, D.
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GMAT 1: 670 Q46 V36
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Re: A certain clock marks every hour by striking a number of times equal  [#permalink]

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30 Oct 2019, 14:03
Bunuel 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

Problem Solving
Question: 110
Category: Arithmetic Operations on rational numbers
Page: 75
Difficulty: 600

The Official Guide For GMAT® Quantitative Review, 2ND Edition

At 6:00:
Total intervals = 11
Time for one interval = x
Time taken = 22
11x = 22 => x = 22/11 = 2

At 12:00
Total intervals = 23
Total time = 23*2 = 46

Re: A certain clock marks every hour by striking a number of times equal   [#permalink] 30 Oct 2019, 14:03

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