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 train leaves in the opposite direction. how many trains will he pass on a complete circuit back to his starting station? do not count trains at the start or end station.

Trains depart after every 4 minutes.
Total time train takes to complete a circuit= 24 minutes
Evan sets off at 8:30 am, so  he will be back at 8:54 am.
So time of trains coming in opposite direction:
8: 34 am
8:38 am
8:42 am
8:46 am
and 8:50 am
5 trains coming in opposite directions.
Now the trains started at 8:06 am from the stations are:
8:06 am
8:10 am
8:14 am
8:18 am
8:22 am
and 8:26 am.
So there are 6 trains started the circuit at 8:06 am.

Now total number of trains=6+5=11 trains

11 trains will pass on complete circuit.