Question 908783
They will flash together at the same time every 60 seconds, ie every minute.


Why 60? Because 60 is the LCM of 12 and 30


Multiples of 12: 12,24,36,48,<font color="green">60</font>,72,84,96,108,120
Multiples of 30: 30,<font color="green">60</font>,90,120,240,270,300


Notice 60 is the smallest multiple they have in common.