Posted by Emma on Tuesday, June 26, 2012 at 11:15pm.
One light flashes every 2 minutes and another light flashes every 3.5 minutes. Suppose both lights flash together at noon. What is the first time after 1 PM that both lights will flash together ?

MATH  Reiny, Wednesday, June 27, 2012 at 7:42am
2 4 6 8 10 12 14 16 18 .....
3.5 7 10.5 14 17.5 ...
looks like they are together (in sync) at
12:14 12:28 12:42 12:56 1:10 1:24 ....
so the first time after 1:00 will be at 1:10