SOLUTION: If I drive 80km at 20kmph and then 60km at 30 kmph how fast must I drive the remaining 40 km, in kilometers per hour, to average 22.5 kmph for the entire trip?

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Question 166104: If I drive 80km at 20kmph and then 60km at 30 kmph how fast must I drive the remaining 40 km, in kilometers per hour, to average 22.5 kmph for the entire trip?
Answer by Mathtut(3670) About Me  (Show Source):
You can put this solution on YOUR website!
total AVERAGE rate of speed for entire trip we will call r=22.5
r1=20---1st 80mi
r2=30---next 60mi
r3=unknown(this is what we are trying to find--- of final 40mi
(r1+r2+r3)/3=r
20+30+r3=3(22.5)
r3=67.5-50
r3=17.5kmph