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Jerry travels 8 miles at an average speed of 40 miles per hour, stops

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Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 28 Jul 2015, 00:52
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Jerry travels 8 miles at an average speed of 40 miles per hour, stops for 10 minutes, and then travels another 20 miles at an average speed of 60 miles per hour. What is Jerry’s average speed, in miles per hour, for this trip?

A. 40
B. 42.5
C. 44
D. 50
E. 52.5

Kudos for a correct solution.

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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 28 Jul 2015, 02:51
1
Time Taken for the first part of the journey= 8/40 = 1/5 hr=12 min

Idle time =10 min

Time Taken for the second part of the journey= 20/60= 1/3 hr =20 min

Total time taken =42 min = 7/10 hr

Total distance = 28 miles

therefore avg speed (28/7)*10 =40 miles per hour

--> : A
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 28 Jul 2015, 03:06
1
Bunuel wrote:
Jerry travels 8 miles at an average speed of 40 miles per hour, stops for 10 minutes, and then travels another 20 miles at an average speed of 60 miles per hour. What is Jerry’s average speed, in miles per hour, for this trip?

A. 40
B. 42.5
C. 44
D. 50
E. 52.5

Kudos for a correct solution.


Total Time taken by jerry = (8/40)*60 Minutes + 10 Minutes + (20/60)*60 Minutes = 42 Minutes

Average Speed = Total Distance / Total Time = (8+20) miles / (42/60)Hours = 28*60 / 42 = 40 Miles per hour

Answer: option A
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 28 Jul 2015, 03:18
2
Bunuel wrote:
Jerry travels 8 miles at an average speed of 40 miles per hour, stops for 10 minutes, and then travels another 20 miles at an average speed of 60 miles per hour. What is Jerry’s average speed, in miles per hour, for this trip?

A. 40
B. 42.5
C. 44
D. 50
E. 52.5

Kudos for a correct solution.


IMO: A

Avg speed = \(\frac{Total distance}{Total time}\)

Total distance = 20+8 = 28 miles
Total time = t1+t2+t3
t1= 8 miles at an average speed of 40 miles per hour ==> 8/40 = 1/5 hr
t2 = 10 minutes idle time = 10/60 = 1/6 hr
t3 = 20 miles at an average speed of 60 miles per hour ==> 20/60 = 1/3 hr
Total time = 1/5 + 1/6 + 1/3 = 7/10

Avg speed = \(\frac{28*10}{7}\) = 40 miles per hr
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 28 Jul 2015, 03:38
1
total distance = 8+20 =28 miles
time = distance/ speed
total time = 8/40 (to go 1st 8 miles) + 10/60 (break) + 20/ 60 (to go 2nd 60 miles)
= 7/10 hours
average speed = total distance / total time
= 28 /(7/10)
=40 miles per hour
ans: A
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 28 Jul 2015, 04:01
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Total distance traveled = \(8+20 = 28\).
Total time taken = \(\frac{60*8}{40} + 10 + 20 = 12 + 10 + 20 = 42\) mins.

Average speed = \(\frac{28*60}{42} = 40\) mph. Ans (A).
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 28 Jul 2015, 05:45
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Average Speed = Total Distance / Total Time

Total distance = 8+20 = 28 miles

Total time = ((8/40)*60) + 10 + ((20/60)*60) = 42 mins = 42/60 hrs

Average speed = (28/42)*60 = 40 miles per hr
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 17 Aug 2015, 08:39
Bunuel wrote:
Jerry travels 8 miles at an average speed of 40 miles per hour, stops for 10 minutes, and then travels another 20 miles at an average speed of 60 miles per hour. What is Jerry’s average speed, in miles per hour, for this trip?

A. 40
B. 42.5
C. 44
D. 50
E. 52.5

Kudos for a correct solution.


800score Official Solution:

Since Rate = Distance/Time, the average rate at which Jerry travels over a certain distance can be found by dividing the total distance of the trip by the total time for the trip.

Let’s find the times for the various portions of the trip using the formula Time = Distance / Rate:
Traveling 8 miles at a speed of 40 miles per hour takes 8/40 = 1/5 hour.
Similarly, traveling 20 miles at 60 miles per hour takes 20/60 = 1/3 hour.
The 10 minutes he was stopped is equal to 1/6 of an hour.

Adding all these times together gives us the total time:
Total time = 1/5 + 1/3 + 1/6
= 6/30 +10/30 + 5/30 = 21/30
= 7/10 hour.

The total distance traveled is 28 miles.

Therefore, the average speed is:
= 28 / (7/10) = 28 × (10/7) = 40 miles per hour.

The correct answer is choice (A).
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 28 May 2018, 18:49
Bunuel wrote:
Jerry travels 8 miles at an average speed of 40 miles per hour, stops for 10 minutes, and then travels another 20 miles at an average speed of 60 miles per hour. What is Jerry’s average speed, in miles per hour, for this trip?

A. 40
B. 42.5
C. 44
D. 50
E. 52.5


Using the formula Average = total distance/total time, we have:

Average = 28/(8/40 + 1/6 + 20/60)

Average = 28/(1/5 + 1/6 + 1/3)

Average = 28/(6/30 + 5/30 + 10/30)

Average = 28/(21/30) = (30 x 28)/21 = (30 x 28)/(3 x 7) = 10 x 4 = 40.

Answer: A
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 20 Oct 2018, 06:42
Total time travelled by Jerry= 60*8/40+10+60*20/60= 12+10+20= 42 mins
Total distance travelled by Jerry= 8+20= 28 miles
Average speed= total distance/total time= 28/42= 2/3 miles per min= 2*60/3= 40 miles per hour.

Ans (A)
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 29 Oct 2018, 13:24
Bunuel wrote:
Jerry travels 8 miles at an average speed of 40 miles per hour, stops for 10 minutes, and then travels another 20 miles at an average speed of 60 miles per hour. What is Jerry’s average speed, in miles per hour, for this trip?

A. 40
B. 42.5
C. 44
D. 50
E. 52.5

Kudos for a correct solution.


Formula: D = RT

Given:

\(D_1 = 8 miles\)
\(R_1 = 40 mph\)
\(T_1 = \frac{{D_1}}{{R_1}} = \frac{{8 miles}}{{40 mph}} = \frac{1}{5}hour\)
Convert minutes to hours because the final answer needs to be in miles per hour
\(T_2 = 10 minutes = \frac{1}{6}hour\)
\(D_3 = 20 miles\)
\(R_3 = 60 mph\)
\(T_3 = \frac{{D_3}}{{R_3}} = \frac{{20 miles}}{{60 mph}} = \frac{1}{3}hour\)
Total distance = 8 miles + 20 miles = 28 miles

Solve:

1. Solve for overall rate using D = RT

2. In order to get total time, find the sum of all provided times: \(T_1 + T_2 + T_3 = \frac{1}{5}hour + \frac{1}{6}hour + \frac{1}{3}hour = (7/10)hour\)

3. \(\frac{D}{T} = \frac{{28 miles}}{(7/10)hour}\) = 40 mph
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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops  [#permalink]

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New post 29 Oct 2018, 14:51
Bunuel wrote:
Jerry travels 8 miles at an average speed of 40 miles per hour, stops for 10 minutes, and then travels another 20 miles at an average speed of 60 miles per hour. What is Jerry’s average speed, in miles per hour, for this trip?

A. 40
B. 42.5
C. 44
D. 50
E. 52.5

Kudos for a correct solution.


T1 = 8/40 = 1/5

Time stopped = 10 mins = 1/6

T2 = 20/60 = 1/3

Total time = 1/5 + 1/3 + 1/6 = 6 + 10 + 5 = 21/30 = 7/10

Avg speed = total distance/total time

= 20 + 8 = 28/(7/10) = (28*10)/7 = 4*10 = 40

Answer choice A

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Re: Jerry travels 8 miles at an average speed of 40 miles per hour, stops &nbs [#permalink] 29 Oct 2018, 14:51
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