A green light blinks every 4 seconds and a yellow light blinks every 5 seconds. At how many seconds will the lights first blink at the same time?

Based on the number of seconds it takes for each light to blink, they will both blink at 20 seconds.

The green light blinks every 4 seconds and the yellow, every 5 seconds.

The time that they will blink together depends on the lowest common multiple of both numbers.

Multiples of 4 = 4, 8, 12, 16, 20

Multiples of 5 = 5, 10, 15, 20

The lowest common multiple is 20 which means they will blink together after 20 seconds.

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20 seconds

Step-by-step explanation:

The least common multiple of 4 and 5 is 20.  So the two lights will blink at the same time every 20 seconds.

step-by-step explanation:

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