A man once had to go by bicycle twelve miles to the railroad station to catch a train. He
thought: 'I have an hour and a half to catch the train. Four miles is uphill, four miles are
downhill, and four miles is level road. I can go uphill at 4 miles per hour, downhill at 12
miles per hour, and I can go 8 miles per hour on level road. This is an average of 8 miles per
hour, so I'll get there in time.' Was his reasoning correct? Why or why not?