Flashing Lights
Flashing Lights printable sheet
Norrie is watching the aircraft warning lights on the tops of some tall buildings in the city. He sees two lights flash at the same time, then one of them flashes every 4th second, and the other flashes every 5th second.
How many times do they flash together during a whole minute?
Norrie then watches a third light. He sees it flash at the same time as the other two, then it flashes every 7th second. How many minutes will it be before this light flashes again at exactly the same time as the other two?
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