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# Two airplanes are 300 miles apart and flying directly toward

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Manager
Joined: 30 Oct 2004
Posts: 132
Two airplanes are 300 miles apart and flying directly toward [#permalink]

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15 Jan 2005, 03:27
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Question Stats:

100% (01:30) correct 0% (00:00) wrong based on 4 sessions

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Two airplanes are 300 miles apart and flying directly toward each other. One is flying at 200 miles per hour, and the other at 160 miles per hour. How long will it take for the two planes to meet?

a) 36 min.
b) 50 min.
c) 1 hour and 12 min.
d) 1 hour and 40 min.
e) 1 hour and 41 min.

Answer and my question in the next post.
Manager
Joined: 30 Oct 2004
Posts: 132

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15 Jan 2005, 03:36

This is how I did the problem:

I set t1 = t2 because it will take both planes the same amount of time to reach one another. Then I use the formula, Time = Distance/Rate, and wrote down the equation:

x/200 = (300-x)/160

with t1=x/200 & t2= (300-x)/160.

I went through the messy algebra and got x= ~167 and substitute into this equation: x/200 and got 0.835, which is = ~ 50 min.

Can anyone think of a simpler way to do this problem?

Questor
CEO
Joined: 21 Jan 2007
Posts: 2739
Location: New York City

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30 Nov 2007, 08:01
This is a Kaplan800 question. Additive rates

OA is B
CIO
Joined: 09 Mar 2003
Posts: 463

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30 Nov 2007, 10:43
bmwhype2 wrote:
This is a Kaplan800 question. Additive rates

OA is B

Right. Whenever you've got two bodies moving in the opposite direction, you can add their rates (you subtract when they're going in the same direction).

So these two planes need to cover 300 miles to meet, at a combined rate of 360 mph.

Then you can use whatever method you want. I think it's safest to use d = rt:
300 = 360t
300/360 = t
5/6 hours =
50 minutes
30 Nov 2007, 10:43
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