Question

On a string of red and blue lights, the red lights blink every 3 seconds, and the blue lights blink every 5 seconds. How many times will they blink at the same time in one minute

Answer 1

So if the red light blinks every 3 seconds and the blue light blinks every 5 seconds, I can indicate that they must both go into something for them to blink at the same time.

So, 3 × 5 = 15. Every 15 seconds they will blink.

There are 60 seconds in a minute, so just divide 60 by 15 to get your answer.

Which will be 4.

The red and blue light will blink 4 times in a minute at the same time.

Answer 2

For this, we must find how many common factors 3 and 5 have under 60. 3*5=15, so multiples of 15 are our key. There are 4 15s in 60, so the answer is 4 times in a minute. Hope this helps!