Question

There is a string of red and blue lights strung around a window. The red lights blink every 3 second and the blue lights every 5 seconds. How many times will they blink at re same time in one minute?

Answer 1

Find the lowest common multiple of 3 and 5, that is 15

the lights will blink together every 15 seconds

in 1 minute blink together
`(60)/(15)` = 4 times

that is at 15, 30, 45 and 60

Answer 2

They will blink 4 times together in one minute.

Explanation:

The amount it takes for them to blink together is the least common multiple between the time it takes for each of them to blink together.

The red light blinks each 3 seconds.

The blue light blinks each 5 seconds.

The least common multiple between 3 and 5 is 15. So they will blink together each 15 seconds.

Each minute has 60 seconds. So they will blink 60/15 = 4 times together in one minute.