Pi and Circles

A diameter must pass through the center of a circle.

• True

• False

Answer explanation

A diameter is a straight line segment that passes through the center of a circle and connects two points on the circle's circumference. Therefore, it is true that a diameter must pass through the center of a circle.

If the diameter of a circle is 9cm, we can ESTIMATE that the circumference will be a little more than:

• 27cm

• 3cm

Answer explanation

The question asks for an estimate of the circumference of a circle with a diameter of 9cm. The formula to calculate the circumference of a circle is π*diameter. Assuming π as 3 (for simplicity), the estimated circumference will be 3*9=27cm. Therefore, the correct choice is a little more than 27cm.

The large circle has radius 9 cm.

The small circle has radius 4 cm.

Find the area of the blue region.

What is the radius of this circle?

• 10

• 20

• 5

• 100