SOLUTION: A truck traveled the first 100 miles of a trip at one speed and the last 135 miles at an average speed of 5 miles per hour less. The entire trip took 5 hours. What was the average

Question 1058175: A truck traveled the first 100 miles of a trip at one speed and the last 135 miles at an average speed of 5 miles per hour less. The entire trip took 5 hours. What was the average speed for the first part of the trip?
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!
D = rt 0r t = D/r
100/r + 135/(r-5) = 5hr
100(r-5) + 135r = 5r(r-5)
5r^2 - 25r - 100r +500 - 135r = 0
5r^2 - 260r + 500 = 0
r^3 - 52r + 100 = 0
(r-50)(r-2) = 0
r = 50mph, the average speed for the first part of the trip
checking:
100mi/50mph + 135mi/45mph = 2hr + 3hr = 5hr CHECKS!
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