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A car has been driven with an average speed of 30 kilometers per hour

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A car has been driven with an average speed of 30 kilometers per hour [#permalink]

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New post 26 May 2016, 12:29
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Difficulty:

  15% (low)

Question Stats:

82% (01:22) correct 18% (01:20) wrong based on 90 sessions

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A car has been driven with an average speed of 30 kilometers per hour during the first 30 kilometers of a journey. Upon reaching the 30th kilometer, the car then travels at 45 kilometers per hour for the next 30 kilometers. Find out the average speed of the car if it has not been stopped at all during the journey.

(A) 35
(B) 36
(C) 37.5
(D) 38
(E) 40
[Reveal] Spoiler: OA

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Re: A car has been driven with an average speed of 30 kilometers per hour [#permalink]

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New post 26 May 2016, 14:35
Bunuel wrote:
A car has been driven with an average speed of 30 kilometers per hour during the first 30 kilometers of a journey. Upon reaching the 30th kilometer, the car then travels at 45 kilometers per hour for the next 30 kilometers. Find out the average speed of the car if it has not been stopped at all during the journey.

(A) 35
(B) 36
(C) 37.5
(D) 38
(E) 40



Avg speed = Total distance/ total time taken
= 60 km/ 100 min
= .6km/m
= .6 * 60 km per hour
ans B
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Re: A car has been driven with an average speed of 30 kilometers per hour [#permalink]

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New post 28 May 2016, 08:57
R * T = D
30 * a = 30 => a=1
45 * b = 30 => b= 2/3

(1*30 + 2/3*90)/5/3 = 36 => B
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Re: A car has been driven with an average speed of 30 kilometers per hour [#permalink]

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New post 09 Dec 2017, 15:25
Formula:
----------
Avg Speed = Total distance / Total Time

d1 = 30
d2 = 30

t1 = 30
t2 = 45

Therefore, 30 + 30 / (30/30 + 30/45)

Avg Speed = 60/1.67 = 35.9 or 36 hence answer is "B" :shocked :thumbup:
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A car has been driven with an average speed of 30 kilometers per hour [#permalink]

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New post 10 Dec 2017, 00:52
Bunuel wrote:
A car has been driven with an average speed of 30 kilometers per hour during the first 30 kilometers of a journey. Upon reaching the 30th kilometer, the car then travels at 45 kilometers per hour for the next 30 kilometers. Find out the average speed of the car if it has not been stopped at all during the journey.

(A) 35
(B) 36
(C) 37.5
(D) 38
(E) 40

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

Total distance is 60 km
We need time for each segment.
RT = D, so T = D/R

For both segments: Time = \(\frac{Distance}{Rate}\)

Time, Segment 1: \(\frac{30km}{30kmh} = 1 hour\)

Time, Segment 2: \(\frac{30km}{45kmh}=\frac{2}{3}hour\)

Total time: \((1 + \frac{2}{3})=\frac{5}{3}hours\)

Average speed=

\(\frac{TotalD}{TotalT}=\frac{60}{(\frac{5}{3})}=(60 * \frac{3}{5})=36\)

Answer B
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A car has been driven with an average speed of 30 kilometers per hour   [#permalink] 10 Dec 2017, 00:52
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