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Manager
Joined: 25 Aug 2009
Posts: 190
Followers: 1
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47
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Re: Noelle walks from point A to point B at an average speed [#permalink]
 13 Sep 2009, 13:46
Question Stats:
0% (00:00) correct
 0% (00:00) wrong based on 0 sessions
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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Intern
Joined: 18 Aug 2009
Posts: 13
Followers: 1
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Re: Noelle walks from point A to point B at an average speed [#permalink]
16 Sep 2009, 02:24
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
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Manager
Joined: 15 Sep 2009
Posts: 149
Followers: 1
Kudos [?]:
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Re: Noelle walks from point A to point B at an average speed [#permalink]
16 Sep 2009, 04:26
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]
16 Sep 2009, 04:26
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