SOLUTION: The green neon lights flash every 5 seconds, the blue every 6 seconds and the red every 7 seconds. If all the lights flash together at 8:00 pm, (a) after how many seconds will they

Algebra ->  Customizable Word Problem Solvers  -> Misc -> SOLUTION: The green neon lights flash every 5 seconds, the blue every 6 seconds and the red every 7 seconds. If all the lights flash together at 8:00 pm, (a) after how many seconds will they      Log On

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Question 990537: The green neon lights flash every 5 seconds, the blue every 6 seconds and the red every 7 seconds. If all the lights flash together at 8:00 pm, (a) after how many seconds will they flash together again? (b) How many times will they flash together in one hour?
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
Greatest common denominator is 5*6*7=210 seconds.
Half won't work, because 6 doesn't divide into 105.
You need a number where 6*7 multiple ends in 5 or 0.
210 seconds is that multiple, or 8:03.30.
3600/210=17.14, so 17 times in an hour.