Question 142042
300/x=70
70x=300
x=300/70
x=4.2857 hours is the total trip time.
100/45+200/x=4.2857
2.22+200/x=4.2857
200/x=4.2857-2.22
200/x=2.06
2.06x=200
x=200/2.06
x=97.09 mph is the required speed for the last 200 miles to average 70 mph for the entire 300 mile trip.
proof:
100/45+200/97.09=300/70
2.22+2.06=4.2857
4.28~4.2857