Question

a red string of holiday lights blinks every 3 seconds while a string of blue lights blink every 4 seconds

Answer 1

I don't know if you had a question to ask, or if you're just giving us
some interesting information about holiday lights.

Either way, here's an interesting piece of information that I can
give you in return:

If you take a string of red lights and a string of blue lights and
turn them both on at exactly the same time, then they'll blink
together every 12 seconds.