<PRE><B>Question 788157</B>
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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