Question 747653
Starting from home,James traveled uphill to the office supply store for 75 minutes for 4 mph. He traveled back home along the same path downhill at a speed of 12 mph. What is the average speed for the entire trip from home to the office supply store and back? 


Distance to supply store = {{{(75/60) * 4}}}, or {{{(5/4) * (4/1)}}}, or 5 miles
Since distance to store is 5 miles, then distance back home = 5 miles also
Therefore, time taken to travel home = {{{5/12}}} hr


Average speed = Total distance ÷ total time


Average speed = {{{(5 + 5)/(5/4 + 5/12)}}} ------- {{{10/(15/12 + 5/12)}}} ------ {{{10/(20/12)}}}


Average speed = {{{10/1}}} ÷ {{{20/12}}} ------  {{{10/1}}} * {{{12/20}}} ------ {{{cross(10)/1}}} * {{{6cross(12)/cross(2)cross(20)}}} ------ {{{6/1}}}, or {{{highlight_green(6)}}} mph