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At 8 AM in the morning, a bell is programmed to sound once after each

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New post 25 Jul 2017, 10:40
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Question Stats:

70% (01:19) correct 30% (00:48) wrong based on 10 sessions

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At 8 AM in the morning, a bell is programmed to sound once after each half hour and an alarm is set to ring after every 70 minutes. At which of the following times during the day did the bell sound and the alarm ring at the same time?

A) 1:30 pm
B) 2:00 pm
C) 6.30 pm
D) 7:40 pm
E) 9:00 pm

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Concentration: General Management, International Business
GMAT 1: 660 Q40 V41
GPA: 3.4
WE: Engineering (Energy and Utilities)
Re: At 8 AM in the morning, a bell is programmed to sound once after each  [#permalink]

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New post 25 Jul 2017, 13:09
duahsolo wrote:
At 8 AM in the morning, a bell is programmed to sound once after each half hour and an alarm is set to ring after every 70 minutes. At which of the following times during the day did the bell sound and the alarm ring at the same time?

A) 1:30 pm
B) 2:00 pm
C) 6.30 pm
D) 7:40 pm
E) 9:00 pm


Bell (half n hour interval) : 8am, 8:30am, 9:00am, 9:30am, 10am, 10:30..... 2:00pm
Alarm (70 mins interval): 8am, 9:10am, 10:20am, 11:30am, 12:40am, 1:50pm, 2:00pm

Answer B
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Re: At 8 AM in the morning, a bell is programmed to sound once after each  [#permalink]

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New post 26 Jul 2017, 02:43
Dkingdom wrote:
duahsolo wrote:
At 8 AM in the morning, a bell is programmed to sound once after each half hour and an alarm is set to ring after every 70 minutes. At which of the following times during the day did the bell sound and the alarm ring at the same time?

A) 1:30 pm
B) 2:00 pm
C) 6.30 pm
D) 7:40 pm
E) 9:00 pm


Bell (half n hour interval) : 8am, 8:30am, 9:00am, 9:30am, 10am, 10:30..... 2:00pm
Alarm (70 mins interval): 8am, 9:10am, 10:20am, 11:30am, 12:40am, 1:50pm, 2:00pm

Answer B


Hi Dkingdom,

I think you made a mistake in your solution, resulting in a wrong answer.

Check your solution again.

According to the sounding time intervals of both the bell and the alarm as shown in your solution, the first time of the day that the bell and the alarm sound at the same time should be 11:30 am, not 2:00 pm. Again, when you add 70 minutes to 1:50 pm, you get 3:00 pm, not 2:00 pm. The next 2 times that both will sound again during the day will be 6:30 pm and 10:00 pm.

Since 6:30 pm is among the answer choices, the correct answer is (C).


Alternatively,

We know that the bell sounds every 30 minutes and the alarm rings every 70 minutes.

To know the time that the bell sounds and the alarm rings at the same time, you can determine the LCM of 30 and 70, which gives 210, implying that at every 210 minutes or 3 hours and 30 minutes, the bell and the alarm sound at the same time.

So starting from 8:00 am, the same sounding times for the bell and the alarm will be 11:30 am, 3:00 pm, 6:30 pm, and 10:00 pm during the day.
_________________
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Joined: 13 Apr 2017
Posts: 82
Location: India
Concentration: General Management, International Business
GMAT 1: 660 Q40 V41
GPA: 3.4
WE: Engineering (Energy and Utilities)
At 8 AM in the morning, a bell is programmed to sound once after each  [#permalink]

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New post 26 Jul 2017, 02:58
duahsolo wrote:
Dkingdom wrote:
duahsolo wrote:
At 8 AM in the morning, a bell is programmed to sound once after each half hour and an alarm is set to ring after every 70 minutes. At which of the following times during the day did the bell sound and the alarm ring at the same time?

A) 1:30 pm
B) 2:00 pm
C) 6.30 pm
D) 7:40 pm
E) 9:00 pm


Bell (half n hour interval) : 8am, 8:30am, 9:00am, 9:30am, 10am, 10:30..... 2:00pm
Alarm (70 mins interval): 8am, 9:10am, 10:20am, 11:30am, 12:40am, 1:50pm, 2:00pm

Answer B


Hi Dkingdom,

I think you made a mistake in your solution, resulting in a wrong answer.

Check your solution again.

According to the sounding time intervals of both the bell and the alarm as shown in your solution, the first time of the day that the bell and the alarm sound at the same time should be 11:30 am, not 2:00 pm. Again, when you add 70 minutes to 1:50 pm, you get 3:00 pm, not 2:00 pm. The next 2 times that both will sound again during the day will be 6:30 pm and 10:00 pm.

Since 6:30 pm is among the answer choices, the correct answer is (C).


Alternatively,

We know that the bell sounds every 30 minutes and the alarm rings every 70 minutes.

To know the time that the bell sounds and the alarm rings at the same time, you can determine the LCM of 30 and 70, which gives 210, implying that at every 210 minutes or 3 hours and 30 minutes, the bell and the alarm sound at the same time.

So starting from 8:00 am, the same sounding times for the bell and the alarm will be 11:30 am, 3:00 pm, 6:30 pm, and 10:00 pm during the day.


AAh.. very silly mistake on my part. Thanks for pointing it out and the alternate explanation. Much appreciated. :)

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.


If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
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At 8 AM in the morning, a bell is programmed to sound once after each   [#permalink] 26 Jul 2017, 02:58
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