Question

Three lightships flash simultaneously at 6;00 a.m. The first lightship flashes every 12 seconds, the seconds lightship every 30 seconds and the third lightship every 66 seconds. At what time will the three lightships next flash together?

• A. 6;09 a.m.
• B. 6:10 a.m.
• C. 6:11 a.m.
• D. 6:12 a.m.

Answer 1

The correct option is C 6:11 a.m.

Three lightships flash simultaneously at 6;00 a.m. The first lightship flashes every 12 seconds, the seconds lightship every 30 seconds and the third lightship every 66 seconds.
Then we take common multiple of 12,30 or 66
That is $2\times 6\times 5\times 11=660$
So the three lightships next flash together=660 seconds =$\frac{660}{60}=11$mints
The time next flash is after 11 mints=6.11 A.M