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25 Jul 2017, 10:40
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Difficulty:
55%
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Question Stats:
86% (02:15) correct
14%
(02:24)
wrong
based on 7
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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
A) 1:30 pm
B) 2:00 pm
C) 6.30 pm
D) 7:40 pm
E) 9:00 pm
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Dkingdom
Joined: 13 Apr 2017
Last visit: 12 Mar 2021
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Location: India
Concentration: General Management, International Business
Schools: INSEAD Jan '19 LBS '19 HEC Jan 2018 Intake IESE '20
GMAT 1: 660 Q40 V41
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WE:Engineering (Energy)
Schools: INSEAD Jan '19 LBS '19 HEC Jan 2018 Intake IESE '20
GMAT 1: 660 Q40 V41
Posts: 69
Kudos:
60
25 Jul 2017, 13:09
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duahsolo
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
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
26 Jul 2017, 02:43
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Dkingdom
duahsolo
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
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.
