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16 Sep 2014, 01:10
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C
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Difficulty:
15%
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Question Stats:
84% (02:09) correct
16%
(02:21)
wrong
based on 118
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If the diameter of each wheel on a car is 0.4 meters, approximately what was the average speed of the car during a three-hour trip, in which each wheel made 100,000 revolutions? (The circumference of a circle is \(2\pi r\), and \(\pi \approx 3.14\))
A. 33 kmh
B. 35 kmh
C. 42 kmh
D. 47 kmh
E. 51 kmh
A. 33 kmh
B. 35 kmh
C. 42 kmh
D. 47 kmh
E. 51 kmh
16 Sep 2014, 01:10
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Official Solution:
If the diameter of each wheel on a car is 0.4 meters, approximately what was the average speed of the car during a three-hour trip, in which each wheel made 100,000 revolutions? (The circumference of a circle is \(2\pi r\), and \(\pi \approx 3.14\))
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. Therefore, the car traveled (number of revolutions)*(circumference) = 100,000 * 1.2 = 120,000 meters or 120 km. Since we used 3 instead of 3.14..., the actual distance traveled is slightly more than 120 km, and thus the actual average speed of the car must be slightly higher than \(\frac{120}{3} = 40\) km/h. Therefore, the best answer is C.
Note: The area of a square, rectangle, the volume of a cube or a rectangular solid, and the Pythagorean theorem are not considered by the GMAT as specific geometry knowledge and can still be tested on the exam. There are several questions involving this in the GMAT Prep Focus mocks. Thus, the question above is not about geometry; it's rather on arithmetic.
Answer: C
If the diameter of each wheel on a car is 0.4 meters, approximately what was the average speed of the car during a three-hour trip, in which each wheel made 100,000 revolutions? (The circumference of a circle is \(2\pi r\), and \(\pi \approx 3.14\))
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. Therefore, the car traveled (number of revolutions)*(circumference) = 100,000 * 1.2 = 120,000 meters or 120 km. Since we used 3 instead of 3.14..., the actual distance traveled is slightly more than 120 km, and thus the actual average speed of the car must be slightly higher than \(\frac{120}{3} = 40\) km/h. Therefore, the best answer is C.
Note: The area of a square, rectangle, the volume of a cube or a rectangular solid, and the Pythagorean theorem are not considered by the GMAT as specific geometry knowledge and can still be tested on the exam. There are several questions involving this in the GMAT Prep Focus mocks. Thus, the question above is not about geometry; it's rather on arithmetic.
Answer: C
01 May 2023, 12:46
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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.
