SOLUTION: John drove his moped from Lansing to Detroit, a distance of 120 km. He drove 10 km per hour faster on the return trip, cutting one hour off of his time. How fast did he drive

Question 788157: John drove his moped from Lansing to Detroit,
a distance of 120 km. He drove 10 km per hour faster on the
return trip, cutting one hour off of his time. How fast did he
drive each way?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
speed there =x
speed return =y
Time going - time return = 1 hour
t=d/r
120/x - 120/(x+10)=1
multiply by x(x+10)
120(x+10)-120x=x^2+10x
120x+1200-120x=x^2+10x
x^2+10x-1200=0
x^2+40x-30x-1200=0
x(x+40)-30(x+40)=0
(x+40)(x-30)=0
x=-40 OR x=30
ignore negative
speed there = 30 km/h
speed return = 40 km/h

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