Average Speed

Question

Julie drives 160 mi to Grandmother's house. On the way to Grandmother's, Julie drives half the distance at 33 mph and half the distance at 58 mph. On her return trip, she drives half the time at 58 mph and half the time at 33 mph.
What is Julie's average speed (in mi/h) on the way to Grandmother's house? What is her average speed (in mi/h) on the return trip?

Answer 1

total distance =160

 

half distance(160/2=80) at 33 mph

time take to cut half distance = t1=distance / speed

t1 = 80/33 = 2.42

 

remaining half distance at 58mph

time take to cut half distance = t2

t2 =80/56 = 1.42

 

average speed = total distance / total time

             

                      =160 /2.42 +1.42

                      

                       = 160 / 3.84

 

                      =41.57 ≈42 mph