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Traveling Word Problem

Two planes left an airport at the same time in opposite directions. One plane flies twice as fast as the other. After 4 hours, they are 2,160 miles apart. How fast is each plane traveling?

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2 Answers

 d = s · t (d - distance in miles, s - speed in miles per hour, t - time in hours)
Let's assume that "s" is the speed of the slower plane, then "2s" is the speed of another one. Because planes are flying in opposite directions, distance between them increases as fast as "s + 2s" mi/hour.
3s · 4 = 2160 ---> 12s = 2160 ---> s = 2160/12 ---> s = 180 mi/h
                                                                            2s = 360 mi/h

Because one plane is traveling twice as fast as the other I would first divide 2,160 by two. You get the sum 1,080. Then divide that by 4. The sum you get is 270. This means that the slower plane is traveling at 270mph. Because the other plane is traveling twice as fast multiply 270 by 2. Then you will find that the faster plane is traveling at 540mph. 


d = (540 + 270) * 4 = 3240 miles !!!!

That is really embarrassing  This is why I shouldn't answer questions late at night. Please don't use my answer!