SOLUTION: A car is driven 850 miles. If it had gone 5.0 miles per hour faster it would have made the trip in 2.0 hour less time. What was the speed?

Question 42340: A car is driven 850 miles. If it had gone 5.0 miles per hour faster it would have made the trip in 2.0 hour less time. What was the speed?
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
850 = r*t
r = 850/t
850 = (r+5)(t-2)
850 = rt + 5t - 2r - 10
850 = t*(850/t) + 5t - 2(850/t) - 10
850 = 850 + 5t - 1700/t -10
-850 = -850
0 = 5t - 1700/t -10
5t - 1700/t = 10
5t^2 -1700 = 10t
5t^2 - 10t - 1700 = 0
t^2 - 2t - 340 = 0
use quadratic formula to find t
then use 850 = rt to find r
at^2 + bt + c = 0

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