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A certain hall contains two cuckoo clocks. If the first

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A certain hall contains two cuckoo clocks. If the first [#permalink] New post 24 Nov 2012, 07:22
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A certain hall contains two cuckoo clocks. If the first clock chirps 20 times per hour and the second clock chirps 10 times per hour, and both clocks begin chirping at 1:15 PM, at what time will the first clock have chirped three times as many times as the second clock can per hour?

A. 1:24 PM
B. 2:05 PM
C. 2:30 PM
D. 2:45 PM
E. 4:15 PM
[Reveal] Spoiler: OA
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Re: A certain hall contains two cuckoo clocks [#permalink] New post 24 Nov 2012, 10:44
I would go with the (D), below I expound upon my choice.
First clcock chirps 20 times per hour , that means 20/60 = 1/3 times per minute.
Second clock chirps 10 times per hour, that would be 10/60 = 1/6 times per minute.
We are asked: at what time will the first clock have chirped three times as many times as the second clock can per hour, or in other words 3 times as many as the second one 3*1/6 = 1/2 and we get the proportion:
1 - 1/3
x - 1/2 from here x = 3/2 =1*(1/2), i.e. 1 hour 30 minutes or 1:15 PM + 1 hour 30 minutes = 2:45
Please, feel free to correct me, if I went awry
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Re: A certain hall contains two cuckoo clocks [#permalink] New post 26 Nov 2012, 07:47
Javoni wrote:
I would go with the (D), below I expound upon my choice.
First clcock chirps 20 times per hour , that means 20/60 = 1/3 times per minute.
Second clock chirps 10 times per hour, that would be 10/60 = 1/6 times per minute.
We are asked: at what time will the first clock have chirped three times as many times as the second clock can per hour, or in other words 3 times as many as the second one 3*1/6 = 1/2 and we get the proportion:
1 - 1/3
x - 1/2 from here x = 3/2 =1*(1/2), i.e. 1 hour 30 minutes or 1:15 PM + 1 hour 30 minutes = 2:45
Please, feel free to correct me, if I went awry


I think your solution makes sense :)
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Re: A certain hall contains two cuckoo clocks [#permalink] New post 26 Nov 2012, 07:56
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I agree with the solution.
So the slower clock can tick 10 times per hour, and according to the problem we want to know when the faster one can potentially tick 10*3 times= 30
Hence 30/20=1.5 or one hour and a half later. Adding this to 1:15 pm the result should be D, or 2:45 pm.
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Re: A certain hall contains two cuckoo clocks. If the first [#permalink] New post 21 Sep 2014, 23:31
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A certain hall contains two cuckoo clocks. If the first [#permalink] New post 23 Sep 2014, 07:41
joylive wrote:
A certain hall contains two cuckoo clocks. If the first clock chirps 20 times per hour and the second clock chirps 10 times per hour, and both clocks begin chirping at 1:15 PM, at what time will the first clock have chirped three times as many times as the second clock can per hour?

A. 1:24 PM
B. 2:05 PM
C. 2:30 PM
D. 2:45 PM
E. 4:15 PM


Good question! Caught me offguard. Notice the highlighted

"at what time will the first clock have chirped three times as many times as the second clock CAN (!!) per hour?"

It is easy to interpret the question as "what time has clock A chirped 3 times more than clock B?" - do some calculations and come up with E

But, We basically want to know when the first clock has chirped 3*10=30 times

Clock A chirps 20 times each hour ----> 1 time each 3min -----> 30 times in 90min

1:15PM + 90min = 2:45PM

Correct Answer: D
A certain hall contains two cuckoo clocks. If the first   [#permalink] 23 Sep 2014, 07:41
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