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If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a

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If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a  [#permalink]

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New post 29 Jun 2018, 01:19
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[GMAT math practice question]

If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a 48 km trip at a constant speed of 30 km/h, what was her average speed, in kilometers per hour, for the two trips?

A. 26 km/h
B. 28 km/h
C. 29 km/h
D. 30 km/h
E. 32 km/h

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Re: If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a  [#permalink]

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New post 29 Jun 2018, 03:29
1
MathRevolution wrote:
[GMAT math practice question]

If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a 48 km trip at a constant speed of 30 km/h, what was her average speed, in kilometers per hour, for the two trips?

A. 26 km/h
B. 28 km/h
C. 29 km/h
D. 30 km/h
E. 32 km/h


Total distance traveled = 10+48=58
Time taken = \(\frac{10}{25}+\frac{48}{30}=2/5 + 8/5=2\)

Speed = 58/2=29 km/h

C
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If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a  [#permalink]

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New post 29 Jun 2018, 03:54
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MathRevolution wrote:
[GMAT math practice question]

If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a 48 km trip at a constant speed of 30 km/h, what was her average speed, in kilometers per hour, for the two trips?

A. 26 km/h
B. 28 km/h
C. 29 km/h
D. 30 km/h
E. 32 km/h


Since Alice travels only a small portion of the total distance at 25 kph but the vast majority of the distance at 30 kph, her average speed for the entire trip must be just a bit less than 30 kph.
Of the five answer choices, only C is sufficiently close to 30 kph.


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If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a  [#permalink]

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New post 29 Jun 2018, 13:07
MathRevolution wrote:
[GMAT math practice question]

If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a 48 km trip at a constant speed of 30 km/h, what was her average speed, in kilometers per hour, for the two trips?

A. 26 km/h
B. 28 km/h
C. 29 km/h
D. 30 km/h
E. 32 km/h

Average speed = \(\frac{TotalDistance}{TotalTime}\)

Trip 1, time, \(T=\frac{D}{r}\)
\(T=\frac{10mi}{25mph}=\frac{2}{5}\) hour

Trip 2, time, \(T=\frac{48mi}{30mph}=\frac{8}{5}\)hour

Total distance: (10 + 48) = 58 miles
Total time: \((\frac{2}{5}+\frac{8}{5})hrs=\frac{10}{5}hrs=2hrs\)

Ave. speed = \(\frac{TotalD}{TotalT}=\frac{58mi}{2hr}=29\) mph

Answer C
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Re: If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a  [#permalink]

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New post 01 Jul 2018, 18:14
=>
The total time taken for the two trips is \(\frac{10}{25} + \frac{48}{30} = 0.4 + 1.6 = 2\) hours.
The total distance traveled on the two trips is \(10 + 48 = 58 km.\)
Thus, the average speed for the two trips is the total distance over the total time, or \(\frac{58}{2} = 29 km / h.\)

Therefore, the answer is C.
Answer: C
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Re: If Alice traveled on a 10 km trip at a constant speed of 25 km/h and a &nbs [#permalink] 01 Jul 2018, 18:14
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