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A certain hall contains two cuckoo clocks. If the first [#permalink]
24 Nov 2012, 07:22

2

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A

B

C

D

E

Difficulty:

65% (hard)

Question Stats:

58% (02:43) correct
42% (02:16) wrong based on 139 sessions

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

Re: A certain hall contains two cuckoo clocks [#permalink]
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 _________________

Re: A certain hall contains two cuckoo clocks [#permalink]
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

Re: A certain hall contains two cuckoo clocks [#permalink]
26 Nov 2012, 07:56

1

This post received KUDOS

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.

Re: A certain hall contains two cuckoo clocks. If the first [#permalink]
21 Sep 2014, 23:31

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A certain hall contains two cuckoo clocks. If the first [#permalink]
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

Re: A certain hall contains two cuckoo clocks. If the first [#permalink]
22 Feb 2015, 10:38

Expert's post

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

Don't be confused by the tricky wording: at its core this is a very simple problem. The second clock chirps 10 times per hour, so we want to know at what point the first clock has chirped three times that, or 3 * 10, which is 30. If the first clock can chirp 20 times per hour, then it will take 1.5 hours to chirp 30 times. 1.5 hours is the same as 90 minutes, so the first clock will have chirped 30 times 90 minutes after 1:15, which would be 2:45 PM. (D). _________________

Re: A certain hall contains two cuckoo clocks. If the first [#permalink]
22 Feb 2015, 11:16

Bunuel wrote:

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

Don't be confused by the tricky wording: at its core this is a very simple problem. The second clock chirps 10 times per hour, so we want to know at what point the first clock has chirped three times that, or 3 * 10, which is 30. If the first clock can chirp 20 times per hour, then it will take 1.5 hours to chirp 30 times. 1.5 hours is the same as 90 minutes, so the first clock will have chirped 30 times 90 minutes after 1:15, which would be 2:45 PM. (D).

Re: A certain hall contains two cuckoo clocks. If the first [#permalink]
22 Feb 2015, 11:20

Lucky2783 wrote:

Bunuel wrote:

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

Don't be confused by the tricky wording: at its core this is a very simple problem. The second clock chirps 10 times per hour, so we want to know at what point the first clock has chirped three times that, or 3 * 10, which is 30. If the first clock can chirp 20 times per hour, then it will take 1.5 hours to chirp 30 times. 1.5 hours is the same as 90 minutes, so the first clock will have chirped 30 times 90 minutes after 1:15, which would be 2:45 PM. (D).

Re: A certain hall contains two cuckoo clocks. If the first [#permalink]
05 Jul 2015, 09:15

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

If we infer that cuckoo chirps evenly per time, than correct answer will be 9 minutes. Because first cuckoo chirps 1 time in 3 minutes and second 1 in 6 minutes. So in 9 minutes first cuckoo shirps 3 times and second 1 time.

If we infer that cuckoo chirps 20 times once in hour than they will chirp simultaneously and this task has no solution: 1 hour 20:10 2 hour 40:20 an so on.

I reread solutions twice but can't understand why we infer that cuckoos chirp two times per hour and make equal number of sounds every half an hour? Am I miss something? _________________

Re: A certain hall contains two cuckoo clocks. If the first [#permalink]
05 Jul 2015, 09:45

1

This post received KUDOS

Harley1980 wrote:

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

If we infer that cuckoo chirps evenly per time, than correct answer will be 9 minutes. Because first cuckoo chirps 1 time in 3 minutes and second 1 in 6 minutes. So in 9 minutes first cuckoo shirps 3 times and second 1 time.

If we infer that cuckoo chirps 20 times once in hour than they will chirp simultaneously and this task has no solution: 1 hour 20:10 2 hour 40:20 an so on.

I reread solutions twice but can't understand why we infer that cuckoos chirp two times per hour and make equal number of sounds every half an hour? Am I miss something?

Hi, Your logic is absolutely correct but we are asked "at what time will the first clock have chirped three times as many times as the second clock can per hour?"... per hour is the catch word.. second clock chirps 10 times in one hour... so the question is basically asking by when will the first clock chirp 30 times (thrice 10 chirps).. first will take 1 hr 30 min for this .. add it to 1:15.. ans 2 :45 ans D hope it helped

Re: A certain hall contains two cuckoo clocks. If the first [#permalink]
05 Jul 2015, 09:53

chetan2u wrote:

Hi, Your logic is absolutely correct but we are asked "at what time will the first clock have chirped three times as many times as the second clock can per hour?"... per hour is the catch word.. second clock chirps 10 times in one hour... so the question is basically asking by when will the first clock chirp 30 times (thrice 10 chirps).. first will take 1 hr 30 min for this .. add it to 1:15.. ans 2 :45 ans D hope it helped

Wow, thanks chetan2u. As usual I miss some crucial words from question ( _________________

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