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4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec

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saswata4s
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4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink] New post   02 Feb 2017, 19:53
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66% (02:26) correct 34% (02:31) wrong based on 255 sessions
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4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 seconds respectively. How many times will they toll together again in the next 3 hours?
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7
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C
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Re: 4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink] New post   02 Feb 2017, 21:09
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All 4 bells toll together at LCM(7, 8, 11, 12) = 1848 secs

3 hours = 3600 * 3 = 10800 secs

Number of times = 10800/1848 --> 5 times

Answer: C
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Re: 4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink] New post   03 Feb 2017, 11:45
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saswata4s wrote:
4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 seconds respectively. How many times will they toll together again in the next 3 hours?
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7


9:00 AM + LCM ( 7, 8, 11 & 12 )

=> 9:00 AM + 1848/60 Min = 9:00 AM +30.80 min

So, The sequence will be 9:00 AM , 9:31 AM , 10 : 02 AM , 10:33 AM, 11:04 AM , 11: 35 AM...

Thus, in the 3 hours, the bells will toll together 5 times...

Hence, answer will be (C) 5
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Re: 4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink] New post   04 Feb 2017, 01:16
saswata4s wrote:
4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 seconds respectively. How many times will they toll together again in the next 3 hours?
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7


This is not a sub-600 level question I'm afraid. To find the LCM of 7, 8, 11, and 12 makes this question roughly an 800 level question. Easy processing but finding the LCM for these 4 numbers is immensely difficult. Reminder: think before you post question difficulty and follow the guidelines
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Re: 4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink] New post   20 Mar 2017, 16:00
Another approach to solve this
The LCM of 7, 8, 11 and 12 seconds is 1848 seconds

Therefore 1848/60 = 30.80

180/30.80 is obviously lower than 6 since 180/30 = 6

Therefore, the answer is C
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Re: 4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink] New post   21 Mar 2017, 03:14
saswata4s wrote:
4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 seconds respectively. How many times will they toll together again in the next 3 hours?
(A) 3
(B) 4
(C) 5
(D) 6
(E) 7


They will toll again after every LCM (7,8,11,12) = 1848 second

no. of times the bell will ring in 3 hrs = 10800 seconds = 10800/1848 = 5.8 or 5 times
adding the first time we get the total no as 6 times.
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Re: 4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink] New post   17 Aug 2021, 11:29
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In order to find the time taken by 4 bells to toll together again after 9 AM, we need to find LCM of (7,8,11,12) secs.

Time taken = LCM of (7,8,11,12) =7*11*24 secs =(7*11*24)/60 minutes = (7*11*2)/5 = 154/5 = 30.8 mins

That means, After 9 AM , all 4 bells will toll together after every 30.8 mins .

Number of times , the bells will toll together again in the next 3 hours = (3*60)/30.8

Since the answer should be an integer, we can approximate it as an integer less than 6 i.e 5

Option C is the answer.

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Clifin J Francis
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Re: 4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink] New post   14 Dec 2023, 07:46
How does one find the LCM of these four numbers?
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Re: 4 Bells toll together at 9:00 A.M. They toll after 7, 8, 11 and 12 sec [#permalink]
14 Dec 2023, 07:46
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