Question 103708: Three lighthouses on three nearby islands flash their lights every evening. On one island, the light flashes every 45 seconds. The secon lighthouse flashes eveery 2 minutes. the third flashes every 1 1/4 minutes. Suppose all three lights flash together at 8:35 pm. At what time will all three lights flash together again?
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website! Three lighthouses on three nearby islands flash their lights every evening. On one island, the light flashes every 45 seconds. The second lighthouse flashes every 2 minutes. the third flashes every 1 1/4 minutes. Suppose all three lights flash together at 8:35 pm. At what time will all three lights flash together again?
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put all the flash times in seconds
45, 120, 75
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Find the LCM (lowest common multiple) of the 3 numbers:
Prime factors will help us do this:
45: 3,3,5
120: 2,2,2,3,5
75: 3,5,5
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LCM: 2*2*2*3*3*5*5 = 1800 secs
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We know 1 hr = 3600 sec, therefore 1800 sec = 1/2 hr
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They will flash simultaneously at 8:35 + :30 = 9:05
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