<PRE><B>Question 521731</B>
amy drove 200 miles at an average speed 10 miles per hour faster than her usual speed. if she completed the trip in 1 hour less time than usual, what is her usual driving speed in miles per hour?
---
Early trip DATA:
distance = 200 miles;  rate = r+10 mph ; time = 200/(r+10) hrs
------------------------
Later trip DATA: 
distance = 200 miles : rate = r mph ; time = 200/r hrs
-------------------------
Equation:
early time - later time = 1 hr
---
200/r - 200/(r+10) =  1 hr.
---
200(r+10) - 200r = r(r+10)
----
200*10 = r^2+10r
----
r^2 + 10r - 2000 = 0
----
(r-40)(r+50) = 0
======================
Positive Solution:
rate = 40 mph
======================
Cheers,
Stan H.
==========
 </PRE>