Airplanes A and B traveled the same 360-mile route

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Airplanes A and B traveled the same 360-mile route [#permalink]

02 Mar 2012, 09:28

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Question Stats:

95% (02:15) correct

4% (00:00) wrong

based on 1 sessions

Airplanes A and B traveled the same 360-mile route. If airplane A took 2 hours and airplane B traveled at an average speed that was \frac{1}{3} slower than the average speed of airplane A, how many hours did it take airplane B to travel the route?

(A) 2

(B) 2\frac{1}{3}

(C) 2\frac{1}{2}

(D) 2\frac{2}{3}

(E) 3

I agree with the OA.
However, something that I don't understand is why cannot analyze it in this way:
The question says that airplane B traveled at an average speed that was \frac{1}{3} slower than the average speed of airplane A, right?
The OE says that, based on this info, that airplane A travels at 180 mph, so airplane B travels at 120 mph (1/3 slower).
Why cannot "1/3 slower" mean this?
A ---- 180 miles / 1 hour
B ---- 180 miles /[(4/3)*1hour]
The answer would be different.

Please, your comments.

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Re: Airplanes A and B traveled the same 360-mile route [#permalink]

02 Mar 2012, 09:47

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metallicafan wrote:

Airplanes A and B traveled the same 360-mile route. If airplane A took 2 hours and airplane B traveled at an average speed that was \frac{1}{3} slower than the average speed of airplane A, how many hours did it take airplane B to travel the route?
(A) 2
(B) 2\frac{1}{3}
(C) 2\frac{1}{2}
(D) 2\frac{2}{3}
(E) 3

I agree with the OA.
However, something that I don't understand is why cannot analyze it in this way:
The question says that airplane B traveled at an average speed that was \frac{1}{3} slower than the average speed of airplane A, right?
The OE says that, based on this info, that airplane A travels at 180 mph, so airplane B travels at 120 mph (1/3 slower).
Why cannot "1/3 slower" mean this?
A ---- 180 miles / 1 hour
B ---- 180 miles /[(4/3)*1hour]
The answer would be different.

Please, your comments.

Source: http://www.gmathacks.com

The red part should be 3/2.

I'd approach this question in different manner and hope that it helps you to understand the question better.

Since B traveled at an average speed that was \frac{1}{3} slower than the average speed of airplane A, then the speed of B was \frac{2}{3} of that of A (x-\frac{1}{3}x=\frac{2}{3}x). So, airplane B would need \frac{3}{2} times more time to cover the same distance: 2*\frac{3}{2}=3 hours. That's because time*rate=distance, so if you decrease rate 2/3 times you'll need 3/2 times as many hours to cover the same distance.

Answer: E.
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Re: Airplanes A and B traveled the same 360-mile route [#permalink] 02 Mar 2012, 09:47

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Airplanes A and B traveled the same 360-mile route

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Airplanes A and B traveled the same 360-mile route

Airplanes A and B traveled the same 360-mile route

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