SOLUTION: Rashard drives 100 mi from Detroit to Lansing, and later drives 90 mi more from Lansing to Grand Rapids. The trip from Lansing to Grand Rapids takes him a half hour less than the d

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Rashard drives 100 mi from Detroit to Lansing, and later drives 90 mi more from Lansing to Grand Rapids. The trip from Lansing to Grand Rapids takes him a half hour less than the d      Log On


   

Question 539007: Rashard drives 100 mi from Detroit to Lansing, and later drives 90 mi more from Lansing to Grand Rapids. The trip from Lansing to Grand Rapids takes him a half hour less than the drive from Detroit to Lansing. What is his driving average speed if it is the same on both parts of the trip?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Rashard drives 100 mi from Detroit to Lansing, and later drives 90 mi more from Lansing to Grand Rapids.
The trip from Lansing to Grand Rapids takes him a half hour less than the drive from Detroit to Lansing.
What is his driving average speed if it is the same on both parts of the trip?
:
Let t = time from Det to Lan
then
(t-.5) = time from Lan to G.R.
:
Write a speed equation, speed = dist/time
Speed was the same on both trips
:
100%2Ft = 90%2F%28%28t-.5%29%29
cross multiply
100(t-.5) = 90t
100t - 50 = 90t
100t - 90t = 50
10t = 50
t = 50/10
t = 5 hrs to Lansing
Find the speed
100/5 = 20 mph was his average speed
check the speed
90/4.5 = 20 mph