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555-605 Level|   Number Properties|         
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At 9:00 a.m., an alarm clock goes off and an annoying person shouts 18 Apr 2022, 06:01
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35% (medium)

Question Stats:

77% (02:32) correct 23% (01:54) wrong based on 102 sessions

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At 9:00 a.m., an alarm clock goes off and an annoying person shouts. If the alarm clock goes off again every 9 minutes and the annoying person shouts every 24 minutes, at which of the following times will both events occur?

(A) 9:35 a.m.
(B) 10:16 a.m.
(C) 11:36 a.m.
(D) 1:48 p.m.
(E) 2:00 p.m.
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D
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CEO2021
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At 9:00 a.m., an alarm clock goes off and an annoying person shouts 29 Apr 2022, 04:47
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GMATNinja
At 9:00 a.m., an alarm clock goes off and an annoying person shouts. If the alarm clock goes off again every 9 minutes and the annoying person shouts every 24 minutes, at which of the following times will both events occur?

(A) 9:35 a.m.
(B) 10:16 a.m.
(C) 11:36 a.m.
(D) 1:48 p.m.
(E) 2:00 p.m.


GMATNinja

chetan2u
LCM of 9 & 24 is 72 thus,both event must have occured after 72 mintures prior 9:00 AM

Please help!!!
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At 9:00 a.m., an alarm clock goes off and an annoying person shouts 29 Apr 2022, 05:31
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GMATNinja
At 9:00 a.m., an alarm clock goes off and an annoying person shouts. If the alarm clock goes off again every 9 minutes and the annoying person shouts every 24 minutes, at which of the following times will both events occur?

(A) 9:35 a.m.
(B) 10:16 a.m.
(C) 11:36 a.m.
(D) 1:48 p.m.
(E) 2:00 p.m.


CEO2021

You are correct in your approach. However, you have misread the question.
The question asks, ‘Which given option would have both actions happening simultaneously?’
So, it is not immediate next but should be the option that fits in.

Alarm clock rings every 9 minutes, and the person shouts every 24 minutes. One such time of the day when both actions are simultaneous is 0900.
They will ring next in LCM(9,24) or in 72 minutes, that is in 1 hour 12 minutes.
So, the difference in option and 0900 h should be multiple of 72 minutes.
I can write down these pretty quickly - 0900, 1012, 1124, 1236, 1348, 1500, 1612, 1724, 1836, 1948, 2100( 09:00pm) so similar time in am and pm.
If calculating in 24 hr format, add 112 when we are looking at a difference of 72 minutes
Only D is in the option

We could also find the difference
(A) 9:35 a.m. ……… 0935-0900 =35….No
(B) 10:16 a.m. ……… 1016-0900 =60+16=76….No
(C) 11:36 a.m. ……… 1136-0900 =2*60+36 = 156….No
(D) 1:48 p.m. ……… 1348-0900 =4*60+48=288=72*4….Yes
(E) 2:00 p.m. ……… 1400-0900 =5*60=300….No


D
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At 9:00 a.m., an alarm clock goes off and an annoying person shouts 29 Apr 2022, 11:19
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A very interesting problem, to say the least – alarm clock going off and annoying person shouting and all – looks like an example for Noise in a Physics text book.

The alarm clock goes off every 9 minutes and the annoying person shouts every 24 minutes. The time taken by the alarm clock is a multiple of 9, while the time after which the annoying person shouts is a multiple of 24. Clearly, there are going to be times when both events occur, these times represent a common multiple of 9 and 24.

Therefore, this is a question on finding the LCM.

The LCM of 9 and 24 = 72. So, both the events occur after every 72 mins; in other words, after every 1 hr 12 mins.

Since we are starting off with 9 AM, we could just look at multiples of 12 i.e., 12, 24, 36, 48, 60 and so on. This actually means, the times after which both events occur are 1hr 12 mins, 2hr 24 mins, 3hr 36mins, 4hr 48 mins and so on.

Clearly, answer option D is the only time that satisfies one of these numbers viz., 4 hr 48 mins.

The correct answer option is D.
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At 9:00 a.m., an alarm clock goes off and an annoying person shouts 02 May 2022, 05:10
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chetan2u
GMATNinja
At 9:00 a.m., an alarm clock goes off and an annoying person shouts. If the alarm clock goes off again every 9 minutes and the annoying person shouts every 24 minutes, at which of the following times will both events occur?

(A) 9:35 a.m.
(B) 10:16 a.m.
(C) 11:36 a.m.
(D) 1:48 p.m.
(E) 2:00 p.m.


CEO2021

You are correct in your approach. However, you have misread the question.
The question asks, ‘Which given option would have both actions happening simultaneously?’
So, it is not immediate next but should be the option that fits in.

Alarm clock rings every 9 minutes, and the person shouts every 24 minutes. One such time of the day when both actions are simultaneous is 0900.
They will ring next in LCM(9,24) or in 72 minutes, that is in 1 hour 12 minutes.
So, the difference in option and 0900 h should be multiple of 72 minutes.
I can write down these pretty quickly - 0900, 1012, 1124, 1236, 1348, 1500, 1612, 1724, 1836, 1948, 2100( 09:00pm) so similar time in am and pm.
If calculating in 24 hr format, add 112 when we are looking at a difference of 72 minutes
Only D is in the option

We could also find the difference
(A) 9:35 a.m. ……… 0935-0900 =35….No
(B) 10:16 a.m. ……… 1016-0900 =60+16=76….No
(C) 11:36 a.m. ……… 1136-0900 =2*60+36 = 156….No
(D) 1:48 p.m. ……… 1348-0900 =4*60+48=288=72*4….Yes
(E) 2:00 p.m. ……… 1400-0900 =5*60=300….No


D

thanks...Kudos !!!(for letting me properly read the stem) :)
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