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Noelle walks from point A to point B at an average speed

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Manager
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Joined: 25 Aug 2009
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Re: Noelle walks from point A to point B at an average speed [#permalink] New post 13 Sep 2009, 12:46
Average speed for the total travel = total distance / total time taken = 6

time taken from A to B, t1 = x/5
time taken to B to A t2 = x/s

where x is the distance b/w A and B and s is the average spped from B to A

=> total distance = 2x
and, total time taken = t1 + t2

=> \frac{2x}{t1 + t2} = 6

=> s = 7.5
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Re: Noelle walks from point A to point B at an average speed [#permalink] New post 16 Sep 2009, 01:24
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The formula for calculating the average speed where 2 different speeds are applied over the same distance is:

[2(S1)(S2)]/(S1+S2], where S1 is the first speed and S2 is the second speed.

In the question, we know S1 = 5 mph and the total overall speed is 6 mph. We just need to find S2.

Hence, plugging in the numbers in the above equation:

[(2)(5)(S2)]/(S1+S1) = 6
[(10)(S2)]/(5+S2)=6
Via cross-multiplication and solving the above equation:
S2=7.5
Manager
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Re: Noelle walks from point A to point B at an average speed [#permalink] New post 16 Sep 2009, 03:26
I wud go with option D)7.5
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Re: Noelle walks from point A to point B at an average speed [#permalink] New post 20 Sep 2014, 21:58
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Re: Noelle walks from point A to point B at an average speed   [#permalink] 20 Sep 2014, 21:58
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Noelle walks from point A to point B at an average speed

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