Area and Circumference From the Diameter

Begin with the radius and diameter sheets, then switch to exact answers in terms of π. Use Circles Maze or Circle Word Problems Review as a self-checking review.

Find the radius, circumference and area for 12 circles from the diameter, from 15.4 cm to 9.9 yd. The directions on the page read: Each row gives the diameter of a circle. Write the radius. Then find the circumference with C = πd and the area with A = πr². Use 3.14 for π, round to the nearest hundredth and include units. The page opens with a worked example, and an answer key is included.

Yes, both. We made it for 8th grade geometry, and it works the same at home or at school. At home, a student can work through it alone and then go over it with you, which shows quickly what is solid and what needs another look. In class it works as independent practice, homework or a warm-up, and you can print one copy or a full set.

Circumference is C = 2πr or C = πd, and area is A = πr². For a radius of 8.5 cm, C is about 53.4 cm and A is about 226.9 cm² with 3.14 for π. Area and Circumference From the Radius opens with this example.

It means you keep the π symbol instead of multiplying by 3.14, so the answer is exact. A circle with a radius of 3.5 cm has a circumference of 7π cm and an area of 12.25π cm². Circle Answers in Terms of Pi and Circle Problems in Terms of Pi practice this.

Divide the area by π, then take the square root. For an area of 50.24 m², 50.24 ÷ 3.14 = 16, so the radius is 4 m. Find the Radius From the Area or Circumference has 12 circles to solve this way.

One full turn rolls a distance equal to the wheel's circumference. A 22 in. wheel turning 40 times rolls 3.14 × 22 × 40 = 2,763.2 in., or about 230.3 ft. Wheels, Tracks and Pizzas starts with this example.