SOLUTION: a car completed a 1000-mile race in 35hr. for the first 600 mile traveled the car averaged 20mph more than it did for the remaining 400 miles traveled. what was the average speed

Question 502012: a car completed a 1000-mile race in 35hr. for the first 600 mile traveled the car averaged 20mph more than it did for the remaining 400 miles traveled. what was the average speed of the car during the first 600 mile travel?
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
a car completed a 1000-mile race in 35hr. for the first 600 mile traveled the car averaged 20mph more than it did for the remaining 400 miles traveled. what was the average speed of the car during the first 600 mile travel
***
let x=average speed of car during first 600 miles of travel.
x-20 =average speed of car during remaining 400 miles of travel.
Travel time=distance/speed
600/x+400/(x-20)=35
LCD: x(x-20)
600(x-20)+400x=35*x(x-20)
600x-12000+400x=35x^2-700x
35x^2-1700x+12000=0
7x^2-340x+2400=0
(let student solve for x using quadratic formula)
ans:
x=8.6 mph (reject, not reasonable)
x=40 mph
The average speed of the car during the first 600 miles of travel=40 mph
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