<PRE><B>Question 1050681</B>
speed going was x mph
time it took to go was 120/x hours, units mi/mi/hr or hr.
speed back was (x+10) mph and its time was 120/(x+10)
(120/x)+(120/(x+10)=7
multiply every thing by x(x+10)
120(x+10)+120x=7x^2+70x, which is 7*x(x+10)
240x+1200=7x^2+70x
7x^2-170x-1200=0
x=(1/14)(170+/- sqrt(170^2+4(8400)); sqrt is of 62500, and that is 250
use positive root only
x=(1/14)(170+250)=(1/14)(420)=30 mph out, 4 hours
x+10=40 mph back or 3 hours. ANSWER


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