Two lights flash at 3 minutes and 8 minutes respectively. If they flash together at 7:00 then at what time next they flash together?

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Solution

To calculate the time at which they flash together we need to find the least common multiple of 3 and 8.
Multiples of 3 =
3 x 1 = 3
3 x 2 = 6
3 x 3 = 9
3 x 4 = 12
3 x 5 = 15
3 x 6 = 18
3 x 7 = 21
3 x 8 = 24
3 x 9 =27
3 x 10 = 30
Multiples of 8 =
8 x 1 = 8
8 x 2 = 16
8 x 3 = 24
8 x 4 = 32
8 x 5 = 40
8 x 6 = 48
8 x 7 = 56
8 x 8 = 64
8 x 9 =72
8 x 10 = 80
So LCM of 3 and 8 = 24
So both the lights will flash next at 7:24

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