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On a radio tower, a red light ﬂashes every 6 seconds and a blue light

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Math Expert
Joined: 02 Sep 2009
Posts: 58445
On a radio tower, a red light ﬂashes every 6 seconds and a blue light  [#permalink]

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03 Dec 2018, 04:53
00:00

Difficulty:

15% (low)

Question Stats:

72% (00:46) correct 28% (01:00) wrong based on 83 sessions

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On a radio tower, a red light ﬂashes every 6 seconds and a blue light ﬂashes every 10 seconds. If both lights ﬂash together at a certain time, how many seconds later will both lights ﬂash together the next time?

A. 6
B. 10
C. 15
D. 30
E. 60

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Joined: 18 Aug 2017
Posts: 5020
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
Re: On a radio tower, a red light ﬂashes every 6 seconds and a blue light  [#permalink]

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03 Dec 2018, 05:47
1
Bunuel wrote:
On a radio tower, a red light ﬂashes every 6 seconds and a blue light ﬂashes every 10 seconds. If both lights ﬂash together at a certain time, how many seconds later will both lights ﬂash together the next time?

A. 6
B. 10
C. 15
D. 30
E. 60

Red light is flashing in multiples of 6 ; 6,12,18,24,30 so on
and blue light in multiples of 10: 10,20,30,40

so question is asking both lights ﬂash together at a certain time, how many seconds later will both lights ﬂash together the next time?

First flash together 30 seconds, 2nd flash together 60 seconds so answer 60-30 = 30
IMO 30 seconds
Intern
Joined: 10 Sep 2018
Posts: 44
Re: On a radio tower, a red light ﬂashes every 6 seconds and a blue light  [#permalink]

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03 Dec 2018, 05:59
1
Let X be the time when the light flashes

X=6I +0
X=10I+0

therefore X= 30I

First flash will be at 30 sec , next will be at 60 sec so the difference will be ( 60-30) = 30 sec
VP
Joined: 31 Oct 2013
Posts: 1465
Concentration: Accounting, Finance
GPA: 3.68
WE: Analyst (Accounting)
Re: On a radio tower, a red light ﬂashes every 6 seconds and a blue light  [#permalink]

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17 Dec 2018, 13:40
1
1
Bunuel wrote:
On a radio tower, a red light ﬂashes every 6 seconds and a blue light ﬂashes every 10 seconds. If both lights ﬂash together at a certain time, how many seconds later will both lights ﬂash together the next time?

A. 6
B. 10
C. 15
D. 30
E. 60

lcm of 6 and 10 is the answer.

lcm( 6, 10) = 30.
Re: On a radio tower, a red light ﬂashes every 6 seconds and a blue light   [#permalink] 17 Dec 2018, 13:40
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