wikiHow Practice Problems to Calculate the Area of a Circle The formula to calculate the area of a circle is A = πr^2, where A is the area and r is the radius of the circle. For example, if the radius of a circle is 4 cm, the area can be calculated as follows: A = π * 4^2 = 16π square cm. Note that π is an irrational number that is approximately equal to 3.14159. To get a more accurate answer, you can use a calculator or mathematical software to perform the calculation. Practice Problems: 1. A circle has a radius of 2 cm. What is the area of the circle? 2. A circle has a diameter of 8 cm. What is the area of the circle? 3. A circular pool has a diameter of 10 meters. What is the area of the pool's surface? 4. A pizza has a diameter of 12 inches. What is the area of the pizza? 5. A metal disk has a radius of 5 cm. What is the area of the disk? 6. A car tire has a radius of 12 inches. What is the area of the contact patch between the tire and the road? 7. A round picnic blanket has a diameter of 6 feet. What is the area of the blanket? Answer Key: 1. Solution: The formula to calculate the area of a circle is A = πr^2, where A is the area and r is the radius of the circle. A = π * 2^2 = 4π square cm. 2. Solution: The diameter of a circle is twice its radius, so the radius can be found by dividing the diameter by 2. In this case, the radius is 8 cm / 2 = 4 cm. A = π * 4^2 = 16π square cm. 3. Solution: The diameter of a circle is twice its radius, so the radius can be found by dividing the diameter by 2. In this case, the radius is 10 meters / 2 = 5 meters. A = π * 5^2 = 25π square meters. 4. Solution: The diameter of a circle is twice its radius, so the radius can be found by dividing the diameter by 2. In this case, the radius is 12 inches / 2 = 6 inches. A = π * 6^2 = 36π square inches. 5. Solution: The formula to calculate the area of a circle is A = πr^2, where A is the area and r is the radius of the circle. A = π * 5^2 = 25π square cm. 6. Solution: The formula to calculate the area of a circle is A = πr^2, where A is the area and r is the radius of the circle. A = π * 12^2 = 144π square inches. 7. Solution: The diameter of a circle is twice its radius, so the radius can be found by dividing the diameter by 2. In this case, the radius is 6 feet / 2 = 3 feet. A = π * 3^2 = 9π square feet. Page