a] David's speed during the period: i] AB speed=distance/time time taken between AB=0.5 hours distance=20 km thus speed=20/0.5=40 km/h
ii]BC time taken between BC=1.5 hours distance=20 speed=20/1.5=13 1/3 km/h
b] Average speed for the entire time will be: average speed=(total distance)/(total time) total distance=(20+20+20)=60 km total time=3 hours thus average speed=60/3=20 km/h
c] David's distance 2 hours and 15 minutes from the starting point was: distance=20+20+10=50 km
