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# ps - wheels (m05q23)

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04 Sep 2008, 10:33
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

A machine consisting of 3 connected wheels is mixing concrete. The engine is running at the speed of 60 rpm and the mixer is mixing at the rate of 8 rpm. What is the diameter of the mixing wheel if the radius of the smaller (drive) wheel is 2 inches?

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04 Sep 2008, 11:10
x2suresh wrote:
A machine consisting of 3 connected wheels is mixing concrete. The engine is running at the speed of 60 rpm and the mixer is mixing at the rate of 8 rpm. What is the diameter of the mixing wheel if the radius of the smaller (drive) wheel is 2 inches?

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I can't image this machine. Could someone explain this or upload the image for me?
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04 Sep 2008, 11:23
Diameter drive wheel = 2*2*pi

Engine rpm = 60

60x4pi (diameter drive wheel) = 240pi

240pi = 8(rpm mix wheel)*pi*diameter(mix wheel)

30inches = diameter mix wheel (answer d)

makes sense?
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04 Sep 2008, 11:24
ans D ? (i m not really sure though)
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04 Sep 2008, 11:51
x2suresh wrote:
A machine consisting of 3 connected wheels is mixing concrete. The engine is running at the speed of 60 rpm and the mixer is mixing at the rate of 8 rpm. What is the diameter of the mixing wheel if the radius of the smaller (drive) wheel is 2 inches?

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I am assuming that smaller wheel is driven directly by the engine at 60 rpm.. i.e speed of smaller wheel is 60 too. in that case using nr=NR i get R=15.

But 3 connected wheel is misleading. It seems to indicate a gear train of 3 wheels.. in that case i cant solve it.
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04 Sep 2008, 14:30
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devilmirror wrote:
x2suresh wrote:
A machine consisting of 3 connected wheels is mixing concrete. The engine is running at the speed of 60 rpm and the mixer is mixing at the rate of 8 rpm. What is the diameter of the mixing wheel if the radius of the smaller (drive) wheel is 2 inches?

12
15
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32

I can't image this machine. Could someone explain this or upload the image for me?

Exactly same feeling. Every one will draw their own picture but I could not draw any Totally blanked.
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04 Sep 2008, 19:09
icandy wrote:
devilmirror wrote:
x2suresh wrote:
A machine consisting of 3 connected wheels is mixing concrete. The engine is running at the speed of 60 rpm and the mixer is mixing at the rate of 8 rpm. What is the diameter of the mixing wheel if the radius of the smaller (drive) wheel is 2 inches?

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I can't image this machine. Could someone explain this or upload the image for me?

Exactly same feeling. Every one will draw their own picture but I could not draw any Totally blanked.

Same here.. that's why I posted this question.. Can some one picture the problem..
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05 Sep 2008, 00:56
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I imagine three wheels connected to each other like the one in a gearbox / transmission.

In this case, if the smallest wheel is of the engine and the largest wheel is of the mixer, then (assuming no transmission loss),

distance travelled by small wheel in one minute = distance travelled by large wheel in one minute.

2*pi*r1*60 = 2*pi*r2*8

or r2 = 15.

However, the question is asking for diameter....hence it will be 30 (although initially I chose the answer as 15 as the value of radius).
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05 Sep 2008, 01:47
Broadly speaking, the ratio of rpm of one wheel to the one directly connected to it is the inverse ratio of the radii.

But from the question, I don't understand which wheel is connected to which. And what does "mixing wheel" or smaller wheel" refer to (smaller than which wheel???)?
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05 Sep 2008, 02:47
x2suresh wrote:
A machine consisting of 3 connected wheels is mixing concrete. The engine is running at the speed of 60 rpm and the mixer is mixing at the rate of 8 rpm. What is the diameter of the mixing wheel if the radius of the smaller (drive) wheel is 2 inches?

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mixing @ 8rpm??
did the people who set the verbal paper set this question by mistake?
wow!!! probably i can also get a chance to set papers...
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12 Nov 2008, 14:29
Here's a pic:

7-p384951?t=54174&hilit=A+machine+consisting+of+3+connected+wheels+is+mixing+concrete#p384951

Atleast I know what a concrete mixing machine looks like now.
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13 Nov 2008, 00:12
A machine consisting of 3 connected wheels is mixing concrete. The engine is running at the speed of 60 rpm and the mixer is mixing at the rate of 8 rpm. What is the diameter of the mixing wheel if the radius of the smaller (drive) wheel is 2 inches?

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engine rate = 60 rpm
mixing rate = 8 rpm
engine rate/ mixing rate = (2 *pi* r of mixer)/ (2*pi*r of engine)
60/8 = r of mixer / r of engine
r of engine>=2
60/8 <= r / 2
r=>15
d = r x 2
d>=30
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Re: ps - wheels (m05q23) [#permalink]

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13 Aug 2009, 06:46
Justed wanted to post an updated version of the question. Hope it's clearer now.

Quote:
A machine consisting of 3 connected wheels is mixing concrete. The engine is running at a speed of 60 rpm and the mixer is mixing at a rate of 8 rpm. If the radius of the smaller (drive) wheel is 2 inches, what is the diameter of the mixing wheel? The smaller wheel is driven directly by the engine.

(C) 2008 GMAT Club - m05#23

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Re: ps - wheels (m05q23) [#permalink]

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23 Nov 2009, 18:44
this question is confusing

How should I know one wheel is an engine? If we are asked 3 wheels we should be told which wheel is which. Just an opinion.
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Re: ps - wheels (m05q23) [#permalink]

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24 Nov 2009, 01:20
The question now makes it clear that the smaller wheel is the drive wheel. I thought the doubts were cleared by adding the "(drive)" part to the question stem. Please tell me what else I can do to make the question clearer.

Thanks.
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Re: ps - wheels (m05q23) [#permalink]

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24 Nov 2009, 08:15
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dzyubam wrote:
The question now makes it clear that the smaller wheel is the drive wheel. I thought the doubts were cleared by adding the "(drive)" part to the question stem. Please tell me what else I can do to make the question clearer.

Thanks.

I don't know if it's the same for everyone but definitely I would need it spelled out for me. xxx made up of 3 wheels, the engine, the drive, and the xxx,the small wheel

In other words, I need to know which wheel is which. Just my opinion. Don't know if the same holds for everyone.
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Re: ps - wheels (m05q23) [#permalink]

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25 Nov 2009, 00:43
Thanks! I'll edit the question if more users find the question confusing. +1.
lagomez wrote:
dzyubam wrote:
The question now makes it clear that the smaller wheel is the drive wheel. I thought the doubts were cleared by adding the "(drive)" part to the question stem. Please tell me what else I can do to make the question clearer.

Thanks.

I don't know if it's the same for everyone but definitely I would need it spelled out for me. xxx made up of 3 wheels, the engine, the drive, and the xxx,the small wheel

In other words, I need to know which wheel is which. Just my opinion. Don't know if the same holds for everyone.

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Re: ps - wheels (m05q23) [#permalink]

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28 Dec 2009, 19:38
A machine consisting of 3 connected wheels is mixing concrete. The engine is running at the speed of 60 rpm and the mixer is mixing at the rate of 8 rpm. What is the diameter of the mixing wheel if the radius of the smaller (drive) wheel is 2 inches?

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After staring at this problem for several minutes I could not come up with anything, so I tried put myself in the shoes of an evil GMAT question writer and tried to imagine what the answer could be. Notice that the question deals with radii. Radii are often converted into diameters by simply multiplying by two. Since diameters are not mentioned in the question, I guessed that there would be a correct answer and a trap answer based on the knowledge that a diameter is twice the length of the radius. Sure enough, there is a pair of answers that fit: 15 and 15 * 2 = 30. I guessed that 15 was the trap answer and 30 was the correct answer. Whammmy!

...if only I were always so lucky!
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25 Mar 2010, 15:08
scthakur wrote:
I imagine three wheels connected to each other like the one in a gearbox / transmission.

In this case, if the smallest wheel is of the engine and the largest wheel is of the mixer, then (assuming no transmission loss),

distance travelled by small wheel in one minute = distance travelled by large wheel in one minute.

2*pi*r1*60 = 2*pi*r2*8

or r2 = 15.

However, the question is asking for diameter....hence it will be 30 (although initially I chose the answer as 15 as the value of radius).

I hope the 3 wheels(gears) are not all connected to each other! This type of machine will not move. LOL
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Re: ps - wheels (m05q23) [#permalink]

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28 Jul 2010, 05:16
This question is terribly confusing. I pictured these three wheels as cogs rotating against one another. Then the ratio (of RPMs) of 60:8 reduces to 15:2. So if the radius of one cog is 2, the radius of the other cog is 15, and the diameter is 30.

I ignored the middle cog. Maybe I lucked out, I'm not sure.
Re: ps - wheels (m05q23)   [#permalink] 28 Jul 2010, 05:16

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# ps - wheels (m05q23)

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