SOLUTION: Hi there, the following problem really has me stumped. Could you help me solve it, please? A jet plane, flying 80mph faster than a propeller plane, travels 3960 miles in 2 hour

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Question 903622: Hi there, the following problem really has me stumped. Could you help me solve it, please?
A jet plane, flying 80mph faster than a propeller plane, travels 3960 miles in 2 hours less time than the propeller plane takes to fly the same distance. How fast does each plane fly?
I ended up solving for "r," in the d=rt formula, and got propeller plane flies at 1956 mph and jet plane 2036 mph. Both answers, however, are incorrect.
Answers cannot have decimals, must either be rounded or fraction form (it's an online homework system).
Thank you!
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39618)   (Show Source): You can put this solution on YOUR website!
Variable assignments could vary but here in use is r for speed of the propeller plane,
t for the time for the propeller plane to do the trip.

______________speed____________time__________distance
JET___________ r+80____________t-2___________3960
PROPLL__________r_______________t____________3960

The rule for uniform travel rates is RT=D for rate time distance;
The system of equations to solve is .
Answer by MathTherapy(10552)   (Show Source): You can put this solution on YOUR website!
Hi there, the following problem really has me stumped. Could you help me solve it, please?
A jet plane, flying 80mph faster than a propeller plane, travels 3960 miles in 2 hours less time than the propeller plane takes to fly the same distance. How fast does each plane fly?
I ended up solving for "r," in the d=rt formula, and got propeller plane flies at 1956 mph and jet plane 2036 mph. Both answers, however, are incorrect.
Answers cannot have decimals, must either be rounded or fraction form (it's an online homework system).
Thank you!


Let speed of propeller plane be S

Then speed of jet = S + 80

Therefore, 

3,960S = 3,960(S + 80) – 2(S)(S + 80) -------- Multiplying by LCD, S(S + 80)











(S – 360)(S + 440) = 0

S, or speed of propeller plane =  mph

Speed of jet = 360 + 80, or  mph  

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