Practice problem
Common-Sense Estimates: Big vs. Small
===

A train track follows a river that winds its way through the countryside. The route is a beautiful scenic journey that takes 8 hours to complete. There is a straight highway that runs parallel to the track and arrives at the same destination. If you drive 60 miles per hour, the journey on the highway will take you 4 hours. About how fast does the train go, in miles per hour?