3lightships flash simultaneously at 6 00 a. m. the first lightship flashes every 12 sec , the second lightship every 30 sec and the third lightship every 66 sec . at what time will the three lightships next flash together

Start Time

6.00am


Find LCM of 12, 30, 66

12 = 2² x 3
30 = 2 x 3 x 5
66 = 2 x 3 x 11
LCM = 2² x 3 x 5 x 11
LCM = 660

⇒ The 3 lights will flash simultaneously again 660 sec later


Convert seconds to minutes

660 sec = 11 min 


Calculate the next time the 3 lightships will flash simultaneously again

6.00 am + 11 mins = 6.11 am


The 3 lightships will flash at 6.11 am again