Question 656622: A jet plane, flying at 130 mph faster than a propeller plane, travels 4550 miles in 4 hours less time than the propeller plane takes to fly the same distance. How fast does each plane fly?
I am having problems with setting up the equation. When I attempted it I got: 4550=(r+130)(t-4) and sub-ed 4550/r for t (d=rt formula). When I solved I got 551.85 and -1071.85. both answers are incorrect. Please help!
Answer by MathTherapy(10555)   (Show Source):
You can put this solution on YOUR website!
A jet plane, flying at 130 mph faster than a propeller plane, travels 4550 miles in 4 hours less time than the propeller plane takes to fly the same distance. How fast does each plane fly?
I am having problems with setting up the equation. When I attempted it I got: 4550=(r+130)(t-4) and sub-ed 4550/r for t (d=rt formula). When I solved I got 551.85 and -1071.85. both answers are incorrect. Please help!
One way to do this problem is to set up a TIME equation, as seen below. This can be done as the difference in their times is 4 hours. What you did which was wrong was set up 2 variables, one for time, and another for speed. We don't need to know individual times. All we need to know, and which we already know is that the difference in travel times between them is 4 hours, and obviously, the jet will take less time than the propeller plane because it's traveling at a faster rate of speed.
Let speed of propeller plane be S
Then speed of jet plane = S + 130
Time jet takes to travel 4,550 miles equals time propeller plane takes to travel 4,550 miles, less 4 hours, OR
 ------ Multiplying by LCD, S(S + 130)
(S + 455)(S - 325) = 0
S = - 455 (ignore), or S, or speed of propeller plane =  mph
Thus, jet plane’s speed = 325 + 130, or  mph
You can do the check!!
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