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A certain car increased its avarage speed by 5 miles per

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A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 08 Feb 2012, 09:11
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A certain car increased its average speed by 5 miles per hour in each successive 5-minute interval after the first interval. If in the first 5-minute interval its average speed was 20 miles per hour, how many miles did the car travel in the third 5-minute interval?

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0

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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 08 Feb 2012, 09:24
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fiendex wrote:
A certain car increased its average speed by 5 miles per hour in each successive 5-minute interval after the first interval. If in the first 5-minute interval its average speed was 20 miles per hour, how many miles did the car travel in the third 5-minute interval?

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0


In the third time interval the average speed of the car was 20+5+5=30 miles per hour;
In 5 minutes (1/12 hour) at that speed car would travel 30*1/12=2.5 miles.

Answer: D.
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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 07 Mar 2012, 09:53
Damn it. Thanks Bunuel.
I calculated the total milage instead of only that of the third segment!! :evil:
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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 21 Apr 2014, 02:01
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Bunuel wrote:
fiendex wrote:
A certain car increased its average speed by 5 miles per hour in each successive 5-minute interval after the first interval. If in the first 5-minute interval its average speed was 20 miles per hour, how many miles did the car travel in the third 5-minute interval?

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0


In the third time interval the average speed of the car was 20+5+5=30 miles per hour;
In 5 minutes (1/12 hour) at that speed car would travel 30*1/12=2.5 miles.

Answer: D.



Had the question asked, how long did the car travel up to third minute interval, how could we have found the answer. Please explain it.
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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 21 Apr 2014, 02:11
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Raihanuddin wrote:
Bunuel wrote:
fiendex wrote:
A certain car increased its average speed by 5 miles per hour in each successive 5-minute interval after the first interval. If in the first 5-minute interval its average speed was 20 miles per hour, how many miles did the car travel in the third 5-minute interval?

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0


In the third time interval the average speed of the car was 20+5+5=30 miles per hour;
In 5 minutes (1/12 hour) at that speed car would travel 30*1/12=2.5 miles.

Answer: D.



Had the question asked, how long did the car travel up to third minute interval, how could we have found the answer. Please explain it.


I guess you mean the total distance covered in three 5-minute intervals.

The distance covered in the first 5-minute interval = (time)(average speed) = 1/12*20;
The distance covered in the second 5-minute interval = (time)(average speed) = 1/12*25;
The distance covered in the third 5-minute interval = (time)(average speed) = 1/12*30.

Total distance = 1/12(20+25+30) = 75/12 miles.
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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 21 Apr 2014, 22:38
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Please refer diagram below

Answer = D
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car.jpg [ 15.09 KiB | Viewed 17060 times ]


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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 27 Apr 2015, 18:21
Hi All,

Here's a similarly-themed question:

the-average-speed-of-a-car-decreased-by-3-miles-per-hour-12994.html#p1520197

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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 20 Jan 2016, 08:34
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Miles per minute on the third interval: 30/60 =1/2. After 5 minutes=( 1/2)*5= 2.5
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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 21 Jan 2016, 05:21
After first 5-minute interval, speed increases to 25 miles per hour
After second 5-minute interval, speed increases to 30 miles per hour
So, in the third 5-minute interval, speed is 30 miles per hour

60 minutes corresponds to 30 miles per hour
So, 5-minutes corresponds to (30/60)*5 = 2.5 miles
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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 18 Feb 2018, 10:39
Quote:
Had the question asked, how long did the car travel up to third minute interval, how could we have found the answer. Please explain it.


I guess you mean the total distance covered in three 5-minute intervals.

The distance covered in the first 5-minute interval = (time)(average speed) = 1/12*20;
The distance covered in the second 5-minute interval = (time)(average speed) = 1/12*25;
The distance covered in the third 5-minute interval = (time)(average speed) = 1/12*30.

Total distance = 1/12(20+25+30) = 75/12 miles.[/quote]

Bunuel how did you calculate time ? :? 1/12 ...does it means that it takes 5 minutes for every 12 miles ? :?
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A certain car increased its avarage speed by 5 miles per  [#permalink]

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A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 19 Feb 2018, 08:54
Bunuel wrote:
dave13 wrote:

Bunuel how did you calculate time ? :? 1/12 ...does it means that it takes 5 minutes for every 12 miles ? :?


5 minutes is 1/12 hour.



hi Bunuel, if i change 5 minutes into 10 minutes interval.

so:
first interval the speed id 20 km per hour
second interval is 30 km per hour
third interval is 40 km per hour

Speed = \(\frac{40 km (distance)}{60 minutes (time)}\)

Time in 10-minute interval, means what distance did the car in 10 minute interval at a speed of 40 km per hour.

Time = \(\frac{distance}{speed}\)

Distance = \(speed * time\) ---> \(\frac{40 km (distance)}{60 minutes (time)}\) * 10 = 6,7 miles

Is my understanding correct ?

thank you :)
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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 21 Feb 2018, 14:12
fiendex wrote:
A certain car increased its average speed by 5 miles per hour in each successive 5-minute interval after the first interval. If in the first 5-minute interval its average speed was 20 miles per hour, how many miles did the car travel in the third 5-minute interval?

A) 1.0
B) 1.5
C) 2.0
D) 2.5
E) 3.0


The rate of the car in the first interval was 20 mph, in the second it was 25 mph, and in the third it was 30 mph.

Since 5 minutes = 5/60 = 1/12 hour, the distance traveled in the third interval was 30 x 1/12 = 30/12 = 5/2 = 2.5 miles.

Answer: D
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Re: A certain car increased its avarage speed by 5 miles per  [#permalink]

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New post 17 May 2019, 20:08
speed = distance * time

speed on 3rd interval = 20+(5+5) = 30

time = speed/distance; (30/60)*5 = 2.5 minutes
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Re: A certain car increased its avarage speed by 5 miles per   [#permalink] 17 May 2019, 20:08
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