Difference between revisions of "2024 AMC 8 Problems/Problem 22"
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==Solution 1== | ==Solution 1== | ||
− | The roll of tape is <math>1/0.015~66</math> layers thick. In order to find the total length, we have to find the average of each concentric circle and multiply it by <math>66</math>. Since the diameter of the small circle is <math>2</math> inches and the diameter of the large one is <math>4</math> inches, the "middle value" is <math>3</math>. Therefore, the average circumference is <math>3\pi</math>. Multiplying <math>3\pi*66 | + | The roll of tape is <math>1/0.015~66</math> layers thick. In order to find the total length, we have to find the average of each concentric circle and multiply it by <math>66</math>. Since the diameter of the small circle is <math>2</math> inches and the diameter of the large one is <math>4</math> inches, the "middle value" is <math>3</math>. Therefore, the average circumference is <math>3\pi</math>. Multiplying <math>3\pi*66</math> gives <math>(B) \boxed{600}</math>. |
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==Solution 2== | ==Solution 2== | ||
There are about <math>\dfrac{1}{0.015}=\dfrac{200}{3}</math> "full circles" of tape, and with average circumference of <math>\dfrac{4+2}{2}\pi=3\pi.</math> <math>\dfrac{200}{3}*3\pi=200\pi, </math> which means the answer is <math>600.</math> | There are about <math>\dfrac{1}{0.015}=\dfrac{200}{3}</math> "full circles" of tape, and with average circumference of <math>\dfrac{4+2}{2}\pi=3\pi.</math> <math>\dfrac{200}{3}*3\pi=200\pi, </math> which means the answer is <math>600.</math> |
Revision as of 16:31, 25 January 2024
Problem 22
A roll of tape is inches in diameter and is wrapped around a ring that is inches in diameter. A cross section of the tape is shown in the figure below. The tape is inches thick. If the tape is completely unrolled, approximately how long would it be? Round your answer to the nearest inches.
(A) (B) (C) (D) (E)
Solution 1
The roll of tape is layers thick. In order to find the total length, we have to find the average of each concentric circle and multiply it by . Since the diameter of the small circle is inches and the diameter of the large one is inches, the "middle value" is . Therefore, the average circumference is . Multiplying gives .
Solution 2
There are about "full circles" of tape, and with average circumference of which means the answer is