Question

George walks 1 mile to school. He leaves home at the same time each day, walks at a steady speed of 3 miles per hour, and arrives just as school begins. Today he was distracted by the pleasant weather and walked the first 12 mile at a speed of only 2 miles per hour. At how many miles per hour must George run the last 12 mile in order to arrive just as school begins today?

Answer 1

Note that on a normal day, it takes him 1/3 hour to get to school. However, today it took 1/2 mile 2 mph=1/4 hour to walk the first 1/2 mile. That means that he has 1/3−1/4=1/12 hours left to get to school, and 1/2 mile left to go. Therefore, his speed must be 1/2 mile1/12 hour=6 mph, so 6 is the answer.