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

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Math Expert
Joined: 02 Sep 2009
Posts: 51229
A car has been driven with an average speed of 30 kilometers per hour  [#permalink]

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26 May 2016, 11:29
00:00

Difficulty:

15% (low)

Question Stats:

84% (01:38) correct 16% (02:29) wrong based on 104 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

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Joined: 12 Mar 2013
Posts: 247
Re: A car has been driven with an average speed of 30 kilometers per hour  [#permalink]

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26 May 2016, 13:35
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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28 May 2016, 07:57
R * T = D
30 * a = 30 => a=1
45 * b = 30 => b= 2/3

(1*30 + 2/3*90)/5/3 = 36 => B
Intern
Joined: 14 May 2016
Posts: 23
Re: A car has been driven with an average speed of 30 kilometers per hour  [#permalink]

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09 Dec 2017, 14:25
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"
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Joined: 22 May 2016
Posts: 2218
A car has been driven with an average speed of 30 kilometers per hour  [#permalink]

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09 Dec 2017, 23:52
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=

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

A car has been driven with an average speed of 30 kilometers per hour &nbs [#permalink] 09 Dec 2017, 23:52
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