They will meet every number of days that is a common multiple of 28 and 36.
The first time they will meet on the train is the LEAST common multiple.
28 = 4*7 = 2*2*7
36 = 4*9 = 2*2*3*3
The LCM must have as many of each factor as either of them have.
So the LCM must have 2 factors of 2, 2 factors of 3, and 1 factor of 7,
So LCM(28,36) = 2*2*3*3*7 = 252. They will meet on the train again in
252 days, which is 36 weeks, (which is somewhere around 8 and a half
months.)
Answer: 252 days, or 36 weeks..
Edwin