SOLUTION: A jet plane, flying 90 mph faster than a propeller plane, travels 3600 miles in 2 hours less time than the propeller plane takes to fly the same distance. How fast does each plane

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Question 1093868: A jet plane, flying 90 mph faster than a propeller plane, travels 3600 miles in 2 hours less time than the propeller plane takes to fly the same distance. How fast does each plane fly?
Answer by josgarithmetic(39618) About Me  (Show Source):
You can put this solution on YOUR website!
                  SPEED         TIME          DISTANCE

JET               r+90         3600/(r+90)     3600

PROPELLER         r            3600/r          3600

Time Difference                 2

3600%2Fr-3600%2F%28r%2B90%29=2
Solve for r and evaluate r+90.
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1800%2Fr-1800%2F%28r%2B90%29=1

common denominator is r%28r%2B90%29.

%281800%2Fr%29r%28r%2B90%29-%281800%2F%28r%2B90%29%29r%28r%2B90%29=r%28r%2B90%29

1800%28r%2B90%29-1800r=r%5E2%2B90r

1800r%2B18%2A9%2A1000-1800r=r%5E2%2B90r

18%2A9%2A1000=r%5E2%2B90r

r%5E2%2B90r-18%2A9%2A1000=0 or highlight_green%28r%5E2%2B90r-162000=0%29

If choose to use general solution for quadratic equation, the discriminant is 810%5E2.

highlight%28r=%28-90%2B810%29%2F2%29------compute and find r+90.
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