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WORD PROBLEM LIGHTHOUSE

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WORD PROBLEM LIGHTHOUSE

by francoisph » Mon May 31, 2010 2:17 pm
Hi guys,

Please could you explain below?

A lighthouse blinks regularly 5 times a minute
A neighboring lighthouse blinks regularly 4 times a minute
If they blink simultaneously, after how many seconds will they blink together again?

thks
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by indiantiger » Mon May 31, 2010 2:25 pm
Lighthouse A blinks 5 times / 60 seconds (or 1 minute)
=> means blinks once every 12 second
Lighthouse B blinks 4 times / 60 seconds (or 1 minute)
=> means blinks once every 15 second

For A , blinks are

12sec,24sec,36sec,48sec,60sec

For B, blinks are

15sec,30sec,45sec,60sec

60 sec (ans)

Let me know if I have done any step wrong
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by gmatjedi » Mon May 31, 2010 4:24 pm
least common multiple principle

factors of 12: 2^2, 3
factors of 15: 3, 5
lcm =2^2*3*5=60
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