Question 1127797

Numbers divisible by 5 are those ending in 5 and 0. Thus, they will blink together every time a multiple of 3 is 5 or 0:
:
3,6,9,12,(15),18,21,24,27,(30),33,36,39,42,(45), 48, 51, 54, 57, (60)
You can count the times, I put them in parenthesis.