[_____10___][_____________100___________][____10____]
Start with the middle section: 100 mi / 60 mph = 5/3 hr.
Now do the end section: 10 mi / 50 mph = 1/5 hr
Add 5/3 + 1/5 = 28/15. Note that is 2/15 short of 30/15, which would be 2 hours. 2/15 of an hour is 8 minutes.
Since the whole trip took 2 hours 22 mins, the first section took 30 mins (8 mins + 22 mins).
30 mins is 1/2 hour, so traveling 10 miles in 30 min would be the rate of 20 mph.
Carcass wrote:
Lorenzo traveled 120 miles by automobile to visit his brother. The first segment of the trip required Lorenzo to drive on 10 miles of city roads before he reached the interstate highway and accelerated to a constant speed of 60 mph. The last segment of the trip was a 10 mile journey over country roads on which Lorenzo averaged 50 miles per hour. If the entire trip took Lorenzo 2 hours and 22 minutes, what was his average speed in miles per hour for the portion of the route between his home and the interstate highway?
KUDOS for the right solution and explanation