Objective: I know how to calculate problems that involve the radius, diameter, circumference and area of circle.

The circumference of a circle is the distance around the circle.

The formula is π*d* or 2π*r
*Read the lesson on circumference of circle if you need to learn how to calculate the circumference of a circle.

The area of a circle is size of the surface of the circle. The formula is π*r*^{2}.

The area of the circle is expressed in square units. Since the formula is only given in terms of radius, remember to change from diameter to radius when necessary.

Read the lesson on area of circle if you need to learn how to calculate the area of a circle.

Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!

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