Question 902629

Jake drives a tractor from one town to another, a distance of 130 kilometers. He drives 9 kilometers per hour faster on the return trip, cutting 1 hour off the time. How fast does he drive each way?
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Let average speed during outbound trip be S
Then average speed during inbound trip is: S + 9
Time equation derived from this: {{{130/S = 130/(S + 9) + 1}}}
130(S + 9) = 130(S) + S(S + 9) -------- Multiplying by LCD, S(S + 9)
{{{130S + 1170 = 130S + S^2 + 9S}}}
{{{130S + 1170 = S^2 + 139S}}}
{{{S^2 + 139S - 130S - 1170 = 0}}}
{{{S^2 + 9S - 1170 = 0}}}
(S - 30)(S + 39) = 0
S, or average speed during outbound trip = {{{highlight_green(30)}}} km//h
Average speed during inbound trip: 30 + 9, or {{{highlight_green(39)}}} km/h
You can do the check!! 

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