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On a certain Monday, Carlos drove to work at an average speed of 50 mi

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On a certain Monday, Carlos drove to work at an average speed of 50 mi  [#permalink]

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New post 05 Nov 2015, 08:08
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On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given

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Re: On a certain Monday, Carlos drove to work at an average speed of 50 mi  [#permalink]

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New post 05 Nov 2015, 21:45
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shasadou wrote:
On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given


To solve the average speed questions, we need to know the total distance and the total time.

Let us assume that the distance from work = D
This will also be the distance from work to home
Hence total distance travelled = 2D

Time in going to work = D/50,
Time in coming back from work = D/70

Hence average speed of both the trips = 2D/ (D/50 + D/70)
= 2*350/12 = 58.33 (Option A)
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Re: On a certain Monday, Carlos drove to work at an average speed of 50 mi  [#permalink]

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New post 05 Nov 2015, 22:06
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shasadou wrote:
On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given



Average Speed if distance covered is the same at two speeds = 2ab/(a+b) = 2*50*70/(50+ 70) = 58.3 miles/hour

For more, check: http://www.veritasprep.com/blog/2015/02 ... -the-gmat/
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On a certain Monday, Carlos drove to work at an average speed of 50 mi  [#permalink]

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New post 11 Aug 2017, 04:44
shasadou wrote:
On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given

Distance is equal; set it at 350.

Leg1 time: 350 mi / 50 mph = 7 hours
Leg2 time: 350/ 70 = 5 hours

Average speed = total distance/total time

700/12 = 58.33

Answer A
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Re: On a certain Monday, Carlos drove to work at an average speed of 50 mi  [#permalink]

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New post 11 Aug 2017, 05:33
For these type of questions we can apply direct formula given below:

2ab/(a+b), where a & b are avg. speed. So 2x50x70/(120)= 58.33 (approx)
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Re: On a certain Monday, Carlos drove to work at an average speed of 50 mi  [#permalink]

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New post 30 Aug 2018, 18:02
shasadou wrote:
On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given


We can use the following formula:

average rate = total distance/total time

If we let the distance each way = d, then the time to work = d/50 and the time from work = d/70. Thus:

average rate = 2d/(d/50 + d/70)

average rate = 2d/(7d/350 + 5d/350)

average rate = 2d/(12d/350)

average rate = (2d x 350)/12d

average rate = 350/6 = 58.3 mph

Answer: A
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Re: On a certain Monday, Carlos drove to work at an average speed of 50 mi  [#permalink]

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New post 08 Jan 2019, 16:25
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shasadou wrote:
On a certain Monday, Carlos drove to work at an average speed of 50 miles per hour and home from work along exactly the same route at an average speed of 70 miles per hour. Which of the following is closest to his average speed for both trips combined?

A. 58.3 miles per hour
B. 60.0 miles per hour
C. 62.6 miles per hour
D. 65.4 miles per hour
E. It cannot be determined from the information given


Average speed = (TOTAL distance)/TOTAL travel time)

Let d = the distance from work to home

Carlos drove to work at an average speed of 50 miles per hour
Time = distance/speed
So, travel time TO work = d/50 hours

Carlos drove home from work at an average speed of 70 miles per hour
So, travel time FROM work = d/70 hours

So, TOTAL travel time = d/50 + d/70
= 7d/350 + 5d/350 [rewrite with common denominators]
= 12d/350

Also, TOTAL distance = d + d = 2d

Which of the following is closest to his average speed for both trips combined?
Average speed = (TOTAL distance)/TOTAL travel time)
= (2d)/(12d/350)
= (2d)(350/12d)
= 700d/12d
= 700/12
= 350/6

STOP.
Since 360/60 = 60, we know that 350/6 will be LESS THAN 60

Answer: A

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Re: On a certain Monday, Carlos drove to work at an average speed of 50 mi   [#permalink] 08 Jan 2019, 16:25
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