Question 214899
Pete drove from Buffalo to Boston, a distance of 720km. On return trip he increased his speed by 10km/h. If the total trip took 17h, what was his speed from Boston to Buffalo? 
I'm having trouble working it out, I begin with this: 
I start with (720/x)+(720/x+10) 
Expanded it to: 17x^2 - 1270x + 7200 
Speed I got next using the quadratic equation: 62.5 
But thats apparently wrong, what am I doing wrong?
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Buff to Bost DATA:
distance = 720 km ; rate = x km/h ; time = d/r = 720/x hrs
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Bost to Buff DATA:
distance = 720 km ; rate = x+10 km/h ; time = 720/(x+10) hrs
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Equation:
time + time = 17 hrs.
(720/x) + (720/(x+10)) = 17
Multiply thru by x(x+10) to get:
720(x+10) + 720(x) = 17x(x+10)
720x + 7200 + 720x = 17x^2 + 170x
17x^2 - 1270x - 7200 = 0
(x-80)(17x + 90) = 0
Positive solution:
x+ 10 = 90 km/h (rate from Boston to Buffalo)
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Cheers,
Stan H.