SOLUTION: Kimberly took three hours to drive to her friend’s home on the weekend. Her average speed was 85 km/h for the first two hours. What was her average speed for the last hour of the t

Algebra ->  Customizable Word Problem Solvers  -> Misc -> SOLUTION: Kimberly took three hours to drive to her friend’s home on the weekend. Her average speed was 85 km/h for the first two hours. What was her average speed for the last hour of the t      Log On

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Question 827967: Kimberly took three hours to drive to her friend’s home on the weekend. Her average speed was 85 km/h for the first two hours. What was her average speed for the last hour of the trip if her average speed was 75 km/h for the whole trip?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Average speed is always:
( total distance ) / ( total time )
Let s = her average speed for the last hr
Her total time was 3 hrs
------------------------
For 1st 2 hrs:
distance = +85%2A2
distance = +170+
------------------
For next hr:
distance = +s%2A1+
------------------
Average for the whole trip:
+75+=+%28+170+%2B+s+%29+%2F+3+
+225+=+170+%2B+s+
+s+=+55+
Her average speed for the last hr was 55 km/hr