Question 1050681: A train traveled 120 miles from Station A to Station B. Then, it immediately returned back to Station A, but at an average speed that is 10 mph faster. The total road trip took 7 hours. How long did it take the train to travel from Station B to Station A?
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! 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
|
|
|
