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Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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13 Sep 2015, 14:24

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Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour?

Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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13 Sep 2015, 14:40

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Let's assume that it takes 4 hours to go from point A to B. Then the distance between them becomes 240 which makes distance between B and C 120. (240+120)/(4+x) gives us the average speed which is 36. You find x=6. So the question simplifies itself to 120/6=20

Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour?

A. 12 B. 20 C. 24 D. 30 E. 36

For average speed, one formula will never fail you:

Average Speed = Total distance/Total Time

Say speed when going from B to C is s. Say distance from B to C is d. So distance from A to B is 2d.

\(36 = \frac{2d + d}{\frac{2d}{60} + \frac{d}{s}}\) d's get cancelled and you get s = 20.

With practice, you will realise that you don't need to take the variable d since it will anyway get cancelled.

Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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26 Sep 2016, 18:04

Hey Guys,

I am having a tough time understanding the explanation of this question...can anyone help?

Thanks!

Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour?

I am having a tough time understanding the explanation of this question...can anyone help?

Thanks!

Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour?

A. 12 B. 20 C. 24 D. 30 E. 36

Merging topics. Please refer to the discussion above.
_________________

Re: Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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26 Sep 2016, 22:15

dre1091 wrote:

Hey Guys,

I am having a tough time understanding the explanation of this question...can anyone help?

Thanks!

Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour?

Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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12 Aug 2017, 08:10

dre1091 wrote:

Hey Guys,

I am having a tough time understanding the explanation of this question...can anyone help?

Thanks!

Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour?

A. 12 B. 20 C. 24 D. 30 E. 36

hi

there is no alternative to understanding the below concept

3d ___________ = 36 2d/60 + d/x

as you see the "d" will get cancelled out, so this understanding is crucial to answering DS questions. For PS questions, however, you can assume small values for distances for your ease of calculations ...

Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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12 Aug 2017, 11:48

sharmasneha wrote:

Tom drives from town A to town B, driving at a constant speed of 60 miles per hour. From town B Tom immediately continues to town C. The distance between A and B is twice the distance between B and C. If the average speed of the whole journey was 36 mph, then what is Tom's speed driving from B to C in miles per hour?

A. 12 B. 20 C. 24 D. 30 E. 36

let 3=total miles r=speed from B to C 3/(2/60+1/r)=36 r=20 mph B

Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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12 Aug 2017, 21:24

average speed formula for 3 equal distances = 3abc/ab+bc+ac where c is the speed for driving from B to C AB is twice of BC, so AB can be divided in 2 equal parts then 3(60*60*c)/(60*60+60c+60c) = 36

Re: Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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13 Aug 2017, 12:24

Let us consider the distance between town A and B is 120. Thus distance between town B and C becomes 60. Since speed from A to B is 60 mph, time taken is \(\frac{120}{60}\) = 2 hrs. Now total distance is 120+60 = 180 and speed is 36 mph, thus total time taken is \(\frac{180}{36}\) = 5 hrs. So to cover 60 miles in remaining 3 hours, he must travel at speed of \(\frac{60}{3}\) = 20 mph
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Abhishek Parikh Math Tutor Whatsapp- +919983944321 Mobile- +971529685639 Website: http://www.holamaven.com

Re: Tom drives from town A to town B, driving at a constant speed of 60 mi [#permalink]

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13 Aug 2017, 19:24

Another easy way to look at this question is Looking at options (knowing average speed is slightly smaller than average(arithmetic mean) of two speeds Calculating average of 60 and all options Option A : average of 60 and 12 = 36, can't be our answer (as average speed cant be equal to average of speeds) Option B : average of 60 and 20 = 40, possible Option C : average of 60 and 24 = 42, way too bigger Option D : average of 60 and 30 = 45, way too bigger Option E : average of 60 and 36 = 46, way too bigger Thus answer is Option B : 20
_________________

Abhishek Parikh Math Tutor Whatsapp- +919983944321 Mobile- +971529685639 Website: http://www.holamaven.com

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