SOLUTION: Consuela biked 20 miles. If she had increased her average speed by 4 miles per hour, the trip would have taken 1 hour less. What is her average speed, in miles per hour?

Question 1189401: Consuela biked 20 miles. If she had increased her average speed by 4 miles per hour, the trip would have taken 1 hour less. What is her average speed, in miles per hour?
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
s*t=distance=20
(s+4)(t-1)=20 but t=20/s, and t-1=(20-s)/s
so (s+4)(20-s)/s=20
20s+80-s^2-4s=20s, multiplying through by s and expanding
s^2+4s-80=0
s=(1/2)(-4 +/- sqrt(16+320));sqrt 336=18.33
s=7.165 mph only positive route
took 2.79 hours to go 20 miles
at 11.165 mph, it would have taken 1.79 hours
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The answer is 7.165 mph
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