Question

a person leaves their house to go to the store. it takes 15 minutes at 12 mph to get to the store. They return home at 31 mph. What is the average rate of the speed for the entire trip?

Answer 1

$\bf \cfrac{\stackrel{speed~forth}{12}+\stackrel{speed~back}{31}}{\stackrel{interval~forth}{1}+\stackrel{interval~back}{1}}\implies \cfrac{43}{2}\implies 21.5mph\textit{ on average}$