wikiHow Practice Problems to Calculate Radius of a Circle 1. Circumference of 36π, find circle's radius. 2. Diameter is 12, what is the radius? 3. Circle's area of 113 sq units, find radius. 4. Circle's circumference of 75.4, find radius. 5. Circle's diameter of 20, determine radius. 6. Circumference of 24π, find circle's radius. 7. Circle's area of 153.94 sq units, find radius. 8. Diameter of 14, determine circle's radius. 9. Circle's circumference of 47.12, find radius. 10. Circle's area of 132 sq units, find radius. Answer key: 1. The radius would be 6. 2. The radius would be 6. 3. he radius would be approximately 3.87298. 4. The radius would be approximately 5. 5. The radius would be 10. 6. The radius would be 4. 7. The radius would be approximately 5.5. 8. The radius would be 7. 9. The radius would be approximately 4.5. 10. The radius would be approximately 6.63324. Page