Question

Susan drove at an average speed of 30 miles per hour for the first 30 miles of a trip and then at an average speed of 60 miles per hour for the remaining 30 miles of the trip. if she made no stops during the trip, what was susan's average speed, in miles per hour, for the entire trip?

Answer 1

The average speed is given by:
average speed=(total distance)/(total time)
total time for the first 30 miles was:
time=distance/speed
=30/30
=1 hr
total time for the remaining 30 miles
=30/60
=0.5
hence the average speed will be:
speed=(30+30)/(1+0.5)=60/1.5=40 miles per hour