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

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Manager
Joined: 25 Aug 2009
Posts: 177
Followers: 1

Kudos [?]: 59 [0], given: 12

Re: Noelle walks from point A to point B at an average speed [#permalink]  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
Intern
Joined: 18 Aug 2009
Posts: 13
Followers: 1

Kudos [?]: 5 [1] , given: 0

Re: Noelle walks from point A to point B at an average speed [#permalink]  16 Sep 2009, 01:24
1
This post received
KUDOS
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
Joined: 15 Sep 2009
Posts: 139
Followers: 1

Kudos [?]: 15 [0], given: 2

Re: Noelle walks from point A to point B at an average speed [#permalink]  16 Sep 2009, 03:26
I wud go with option D)7.5
SVP
Joined: 09 Sep 2013
Posts: 2455
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Kudos [?]: 38 [0], given: 0

Re: Noelle walks from point A to point B at an average speed [#permalink]  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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