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M21-12

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M21-12  [#permalink]

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New post 16 Sep 2014, 01:10
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

81% (01:37) correct 19% (01:42) wrong based on 148 sessions

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Math Expert
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Re M21-12  [#permalink]

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New post 16 Sep 2014, 01:10
1
Official Solution:

If the diameter of each of a car's wheels is 0.4 meters, approximately, what was the average speed of the car for its three-hour trip in which each wheel made 100,000 revolutions?

A. 33 kmh
B. 35 kmh
C. 42 kmh
D. 47 kmh
E. 51 kmh

The circumference of the wheel is \(0.4\pi\) or approximately 1.2 meters. The car went \(100,000*1.2\) meters or \(100*1.2 = 120\) km. Because we used 3 instead of 3.14, the actual average speed of the car must be somewhat higher than \(\frac{120}{3} = 40\)kmh. The best answer is C.

Answer: C
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Re: M21-12  [#permalink]

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New post 16 Oct 2018, 19:07
I feel this solution is wrong.

Total distance without rounding off = 40*3.414 km
Avg Speed = 40*3.414/3 = 45.52km/hr
None of the options has the answer.
In this case, Option D is the closest possible choice.
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Re: M21-12  [#permalink]

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New post 16 Oct 2018, 20:53
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Re: M21-12  [#permalink]

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New post 16 Oct 2018, 23:33
Bunuel wrote:
sarvesh93sah wrote:
I feel this solution is wrong.

Total distance without rounding off = 40*3.414 km
Avg Speed = 40*3.414/3 = 45.52km/hr
None of the options has the answer.
In this case, Option D is the closest possible choice.

__________________________
\(\pi = 3.141...\), not 3.414.

I am sorry.....My bad
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Re: M21-12   [#permalink] 16 Oct 2018, 23:33
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M21-12

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