Averaged speed City A to City B

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Averaged speed City A to City B

by deepoe » Wed Mar 04, 2009 9:04 am
The distance between cities A and B is 120 miles. A car travels from A to B at 60 miles per hour and returns from B to A along the same route at 40 miles per hour. What is the averaged speed for the round trip?

A. 48
B. 50
C. 52
D. 56
E. 58

OA = A

12 / 6 = 24 / 12
12 / 4 = 36 / 12

60 / 12 = 5 H

120 / 5 = 24 M/H

What did I wrong?
Source: — Problem Solving |

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by deepoe » Wed Mar 04, 2009 9:08 am
Oh nevermind! I already saw it!!! Need to divide 240 with 5 :$ :oops:

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by marcusking » Wed Mar 04, 2009 9:17 am
deepoe wrote:Oh nevermind! I already saw it!!! Need to divide 240 with 5 :$ :oops:
This is a common problem that I struggle with too when I'm going to fast. :)

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by farooq » Wed Mar 04, 2009 9:42 am
marcusking wrote:
deepoe wrote:Oh nevermind! I already saw it!!! Need to divide 240 with 5 :$ :oops:
This is a common problem that I struggle with too when I'm going to fast. :)
If distance is same, then we can apply formula.

Average Speed = (2 * S1 *S2)/S1 + S2
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by Ian Stewart » Wed Mar 04, 2009 7:33 pm
Here you could also notice:

-the distances are the same for each part of the trip;
-the car will thus certainly spend more time traveling at the slower speed;
-so the answer must be closer to 40 than to 60.

Looking at the answers, only 48 is possible.
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