Answer:
After 120 seconds
Step-by-step explanation:
Here, we want to know the number of seconds after which both spotlights will change colors at the same time again.
Basically, what we want to do here is to
calculate the value with which 30 and 40 have the same multiples or we want to
calculate the lowest common multiple of 30 and 40
The multiples of 30 are 30,60,90,120 etc
The multiples of 40 are 40,80,120 etc
We can see that the lowest common multiple of both is 120
So therefore the spotlights will change colors at the same time after 120 seconds
