Area of an Annulus Worksheet
Calculate the area of an annulus using given radii for Grade 9 geometry students.
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Area of an Annulus
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Read each question carefully and calculate the area of the annulus. Show all your work. Use π ≈ 3.14 where necessary and round your answers to two decimal places.
An annulus is the region between two concentric circles. Its area can be calculated by subtracting the area of the inner circle from the area of the outer circle. The formula for the area of an annulus is A = π(R² - r²), where R is the radius of the outer circle and r is the radius of the inner circle.
1. An annulus has an outer radius of 10 cm and an inner radius of 6 cm. Calculate its area.
2. If the area of an annulus is 75.36 cm² and its inner radius is 4 cm, then its outer radius (R) is approximately cm. (Use π ≈ 3.14)
3. Which of the following formulas correctly represents the area of an annulus?
A = πr²
A = π(R + r)²
A = π(R² - r²)
A = 2πR
4. A circular pathway is built around a circular fountain. The fountain has a radius of 3 meters, and the pathway is 2 meters wide. What is the area of the pathway?
5. An annulus can also be referred to as a circular ring.
True
False
6. A metal washer has an outer diameter of 30 mm and an inner diameter of 10 mm. Find the area of one side of the washer.