SOLUTION: Rodney Racer averages 90mph in the first lap of a race. How fast must he go in the second half in order to average 120mph for the whole race?

Question 532865: Rodney Racer averages 90mph in the first lap of a race. How fast must he go in the second half in order to average 120mph for the whole race?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Rodney Racer averages 90mph in the first lap of a race.
How fast must he go in the second half in order to average 120mph for the whole race?
:
Let s = speed required to average 120 mph
d = one lap distance
:
Write a time equation; time = dist/speed
:
+ =
reduce the third fraction
+ =
Multiply by 180s to get rid of the denominators, results
2ds + 180d = 3ds
simplify, divide by d
2s + 180 = 3s
180 = 3s - 2s
180 = s
He has to run 180 mph to average 120 for the two laps
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