A circular rim 28 inches in diameter rotates the same number

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A circular rim 28 inches in diameter rotates the same number [#permalink]

08 Jun 2008, 12:01

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Question Stats:

41% (02:50) correct

58% (02:03) wrong

based on 16 sessions

[Reveal] Spoiler: OA

Last edited by Bunuel on 22 Jan 2013, 07:39, edited 1 time in total.

Renamed the topic, edited the question and added the OA.

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Re: circular rim [#permalink]

08 Jun 2008, 14:17

I want to pick 48x, but choice B stands out from the rest, so B it is.

puma wrote:

A circular rim 28 inches in a diameter rotates the same number of inches per second as a circular rim 35 inches in diameter. If the smaller rim makes X revilutions per second, how many revilutions per minute does the larger rim makes in terms of X?

a) 48pi/x
b) 75m
c) 48x
d) 24x
e) x/75

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Re: circular rim [#permalink]

08 Jun 2008, 22:44

puma wrote:

circumference * (rev/min) of 28 =circumference * (rev/min) of 35
to calculate z
pi*28*x=pi*35*z
z=4/5 * x
but this is inch/sec we want inch/min

z=4/5 * x*60
=48x

C

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Re: circular rim [#permalink]

30 Jul 2009, 14:44

thanks for the explanation.

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Re: circular rim [#permalink]

01 Aug 2009, 11:20

let's say no. of revolution made by the larger rim = n/sec
28 *pi*x= 35*pi*n
therefore, n= (28*pi*x)/(35*pi)=4x/5
so in 1 min no of revolution = 60*(4x/5)=48x

so C

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Re: A circular rim 28 inches in a diameter rotates the same [#permalink]

22 Jan 2013, 07:29

How to solve this question? IS this a rates problem?

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Re: A circular rim 28 inches in a diameter rotates the same [#permalink]

22 Jan 2013, 07:59

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fozzzy wrote:

How to solve this question? IS this a rates problem?

A circular rim 28 inches in diameter rotates the same number of inches per second as a circular rim 35 inches in diameter. If the smaller rim makes x revolutions per second, how many revolutions per minute does the larger rim makes in terms of x ?

A. 48pi/x
B. 75x
C. 48x
D. 24x
E. x/75

1 revolution of a circle = circumference of that circle.

1 revolution of a circle with the diameter of 28 inches = \pi{d}=28\pi inches. Hence, x revolutions per second = 28\pi{x} inches per second = 60*28\pi{x} inches per minute.

Given that 60*28\pi{x}=35\pi{n} --> n=\frac{60*28\pi{x}}{35\pi}=48x.

Answer: C.

Hope it's clear.
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Re: A circular rim 28 inches in diameter rotates the same number [#permalink]

03 Apr 2013, 14:13

Ahem;

You don't need to involve pi - it's a constant that has no bearing on the solution.

The question is really just simple arithmetic - the sort of question that used to be posed to ten year olds.

If rim speeds are the same, and the small rim is rotating at x rps, then the large rim would be rotating at 28x/35 rps, or 60 x 28x/35 rpm = 48x rpm

Re: A circular rim 28 inches in diameter rotates the same number [#permalink] 03 Apr 2013, 14:13

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A circular rim 28 inches in diameter rotates the same number

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A circular rim 28 inches in diameter rotates the same number

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