Joe gets up in the morning whenever he wakes up, rubs his eyes, jumps out of bed and runs down to the train station to jump on the first train that arrives to go to work.
It is a one-track station and trains have a 20 minute interval between their respective arrivals.
The problem is that nine out of ten times Joe arrives in the wrong city. Soon he will get fired for coming late to work so often.
How is this possible?