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M07-36

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Bunuel
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M07-36 [#permalink] New post   16 Sep 2014, 00:36
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84% (01:11) correct 16% (01:36) wrong based on 85 sessions
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If each blade of a windmill is 10 meters long and the endpoints of the blades rotate at a speed of \(100\pi\) meters per minute, how many revolutions per minute do the blades make?

A. 2
B. 3
C. 4
D. 5
E. 6
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D
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Bunuel
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Re M07-36 [#permalink] New post   16 Sep 2014, 00:36
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Official Solution:

If each blade of a windmill is 10 meters long and the endpoints of the blades rotate at a speed of \(100\pi\) meters per minute, how many revolutions per minute do the blades make?

A. 2
B. 3
C. 4
D. 5
E. 6


The circumference of a circle with a radius of 10 meters is \(20\pi\) meters, so each endpoint travels a distance of \(20\pi\) meters in one revolution. Given that the endpoints of the blades rotate at a speed of \(100 \pi\) meters per minute, they complete \(\frac{100 \pi}{20 \pi} = 5\) revolutions per minute.


Answer: D
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Re: M07-36 [#permalink] New post   01 Jan 2016, 02:50
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Distance traveled in one rotation = Circumference = 2πR = πD =20 π
If blade tip travels 100 π in a minute means it has rotated 100π/20π = 5 times.
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Re: M07-36 [#permalink] New post   01 Feb 2017, 00:22
hi
kindly explain why radius is 10?its given that diameter is 10 so radius has to be 5??
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Re: M07-36 [#permalink] New post   01 Feb 2017, 00:44
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gupta87 wrote:
hi
kindly explain why radius is 10?its given that diameter is 10 so radius has to be 5??


Check the image below. It's given that the blades of a windmill are 10 meters long each. The blades are radii there.
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1-5mw-Windmill-Generator.jpg
1-5mw-Windmill-Generator.jpg [ 38.04 KiB | Viewed 17345 times ]

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Re: M07-36 [#permalink] New post   01 May 2023, 13:12
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I have edited the question and the solution by adding more details to enhance its clarity. I hope it is now easier to understand.
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RajibDhara
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Re: M07-36 [#permalink] New post   21 Apr 2024, 10:17
Bunuel wrote:
If each blade of a windmill is 10 meters long and the endpoints of the blades rotate at a speed of \(100\pi\) meters per minute, how many revolutions per minute do the blades make?

A. 2
B. 3
C. 4
D. 5
E. 6

­Is this a gmat focus type question ?
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Bunuel
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Re: M07-36 [#permalink] New post   21 Apr 2024, 10:25
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RajibDhara wrote:
Bunuel wrote:
If each blade of a windmill is 10 meters long and the endpoints of the blades rotate at a speed of \(100\pi\) meters per minute, how many revolutions per minute do the blades make?

A. 2
B. 3
C. 4
D. 5
E. 6

­Is this a gmat focus type question ?


Yes, I believe so. 
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Re: M07-36 [#permalink]
21 Apr 2024, 10:25
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Bunuel
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