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# A machine consisting of 3 connected wheels is mixing

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CEO
Joined: 21 Jan 2007
Posts: 2734

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Location: New York City
A machine consisting of 3 connected wheels is mixing [#permalink]

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19 Oct 2007, 12:58
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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.

What is the diameter of the mixing wheek if the radius of the smaller drive wheel is 2 inches?

12

15

25

30

32

Kudos [?]: 1091 [0], given: 4

Director
Joined: 22 Aug 2007
Posts: 566

Kudos [?]: 79 [0], given: 0

Re: PS hard RT=D question [#permalink]

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19 Oct 2007, 13:19
bmwhype2 wrote:
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.

What is the diameter of the mixing wheek if the radius of the smaller drive wheel is 2 inches?

12

15

25

30

32

i still wonder how is someone who never bothered to look carefully at the structure of concrete mixing machine in his/her entire life supposed to solve this question... and are not there different types of concrete mixing machines...

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VP
Joined: 08 Jun 2005
Posts: 1141

Kudos [?]: 257 [0], given: 0

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19 Oct 2007, 13:31
I would say (D)

Since the smaller circle has radius of 2 then its perimeter is 4pi

every minute it goes a way of 4pi*60 = 240pi

the biggest circle perimeter is unknown 2*pi*r

240*pi = 2*pi*r*8

r = 15

so the diameter is 30

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Current Student
Joined: 28 Dec 2004
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Schools: Wharton'11 HBS'12

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20 Oct 2007, 08:42
ahh.. good one..i fell for 15...

30 is correct..we are looking for diam.

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CEO
Joined: 21 Jan 2007
Posts: 2734

Kudos [?]: 1091 [0], given: 4

Location: New York City

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19 Dec 2007, 08:04
KillerSquirrel wrote:
I would say (D)

Since the smaller circle has radius of 2 then its perimeter is 4pi

every minute it goes a way of 4pi*60 = 240pi

the biggest circle perimeter is unknown 2*pi*r

240*pi = 2*pi*r*8

r = 15

so the diameter is 30

OA is D 30

Kudos [?]: 1091 [0], given: 4

19 Dec 2007, 08:04
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