Math Problem Statement

Both circles have the same center. The circumference of the inner circle is 12.56 inches. What is the area of the shaded region?

C

=

12.56 in

3 in

Solution

To solve this problem, we need to determine the area of the shaded region between the two concentric circles.

Step 1: Find the radius of the inner circle.

The circumference CC of a circle is given by the formula:

C=2πrC = 2\pi r

Given that the circumference of the inner circle is 12.5612.56 inches, we can solve for the radius rr:

12.56=2πr12.56 = 2\pi r

r=12.562π=12.566.28=2 inchesr = \frac{12.56}{2\pi} = \frac{12.56}{6.28} = 2 \text{ inches}

So, the radius of the inner circle is 22 inches.

Step 2: Determine the radius of the outer circle.

The problem states that the outer circle has a radius of 33 inches.

Step 3: Calculate the area of both circles.

The area AA of a circle is given by the formula:

A=πr2A = \pi r^2

  • Inner circle area: Ainner=π×(2)2=π×4=12.56 square inchesA_{\text{inner}} = \pi \times (2)^2 = \pi \times 4 = 12.56 \text{ square inches}

  • Outer circle area: Aouter=π×(3)2=π×9=28.26 square inchesA_{\text{outer}} = \pi \times (3)^2 = \pi \times 9 = 28.26 \text{ square inches}

Step 4: Calculate the area of the shaded region.

The shaded region is the difference between the area of the outer circle and the inner circle:

Ashaded=AouterAinner=28.2612.56=15.7 square inchesA_{\text{shaded}} = A_{\text{outer}} - A_{\text{inner}} = 28.26 - 12.56 = 15.7 \text{ square inches}

Final Answer:

The area of the shaded region is 15.7 square inches.

Would you like further details or have any questions?


Here are 5 related questions for you to explore:

  1. What is the formula for finding the area of a sector in a circle?
  2. How do you find the circumference of a circle given its radius?
  3. What is the relationship between the diameter and the radius of a circle?
  4. How do you calculate the area of a circle if only the circumference is known?
  5. How does the area of a circle change if the radius is doubled?

Tip: When working with concentric circles, always subtract the area of the smaller circle from the larger to find the area of the ring-shaped region between them.

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Math Problem Analysis

Mathematical Concepts

Geometry
Circle properties

Formulas

Circumference of a circle
Area of a circle

Theorems

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Suitable Grade Level

High School