SOLUTION: Trains on the Glasgow Subway depart every 4 minutes, and a complete circuit takes 24 minutes. Ewan sets off at 8.30 am on a train round in one direction at the same time as another

First, you should count those trains that started at or after 8:30 am in the opposite direction.

There are 6 of them that started at 8:30 am, 8:34 am, 8:38 am, 8:42 am, 8:46 am and 8:50 am.


In addition to it, you should count those trains that started before 8:30 in the opposite direction and arrived 
to the starting/ending station after 8:30 am.


Ewan will meet those trains too.    (Accounting for these trains and not missing them is the major point of the solution to this problem !)


These are the trains that 

started at 8:06 am     arrived at 8:30 am     (should not be counted)

           8:10 am                8:34 am     (counts)

           8:14 am                8:38 am     (counts)

           8:18 am                8:42 am     (counts)

           8:22 am                8:46 am     (counts)

           8:24 am                8:50 am     (counts)


The number of such trains is  5.


So, the total is  6 + 5 = 11, and I do not count the trains at the start or end station, as the condition requires.