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PS: Common type of question

by Vishnu88 » Tue Apr 19, 2011 10:46 am
Two airplanes are 300 miles apart flying directly toward each other. One is flying at 200 miles per hr and the other at 160 miles per hr. how long will it take for the two to meet?

An easy strategy to follow for this kind of question will be much appreciated. Cheers!

a. 36 mins
b. 50 mins
c. 1 hr 12 mins
d. 1 hr 40 mins
e. 1 hr 41 mins
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by pemdas » Tue Apr 19, 2011 10:57 am
the distance between two airplanes is D, D=300
two airplanes fly directly toward each other means their combined distances will be equal to D or 300
we need to find time when two airplanes meet - only one time, momentum, hence t(1)=t(2) or simply T
D(1)+D(2)=D and 200*T + 160*T = D since time is one value for both airplanes
360*T=300, T=300/360, T=5/6 hour or 50 minutes

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Vishnu88 wrote:Two airplanes are 300 miles apart flying directly toward each other. One is flying at 200 miles per hr and the other at 160 miles per hr. how long will it take for the two to meet?

An easy strategy to follow for this kind of question will be much appreciated. Cheers!

a. 36 mins
b. 50 mins
c. 1 hr 12 mins
d. 1 hr 40 mins
e. 1 hr 41 mins
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by Tani » Tue Apr 19, 2011 11:07 am
You can also eyeball this one. In one hour the two planes will have traveled 360 miles - too far, so that leaves out C,D, and E.

Looking at the other two answers, your 360 is pretty close to 300, so the answer will be fairly close to one hour - 50 minutes works.
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by GMATGuruNY » Tue Apr 19, 2011 1:33 pm
Vishnu88 wrote:Two airplanes are 300 miles apart flying directly toward each other. One is flying at 200 miles per hr and the other at 160 miles per hr. how long will it take for the two to meet?

An easy strategy to follow for this kind of question will be much appreciated. Cheers!

a. 36 mins
b. 50 mins
c. 1 hr 12 mins
d. 1 hr 40 mins
e. 1 hr 41 mins
When elements work together to complete a task or to travel a distance, we can add their rates.

Since the two planes are traveling toward each other, they are working together to travel the distance of 300 miles.
Their combined rate = 200+160 = 360 miles per hour.
Time = d/r = 300/360 = 5/6 hours = 50 minutes.

The correct answer is B.
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by Tani » Tue Apr 19, 2011 5:10 pm
Conversely, if they were traveling in the same direction we would subtract their rates.
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by m.abdulk » Wed Apr 20, 2011 11:46 am
if they meet after time t then in this duration , the sum of the distances traveled by both should be 300
200*t+160*t=300
t=300/360 hrs
or t=(300*60)/360 mins = 50mins.
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