Circumference and Area of Circles

Front

What is the formula for the circumference of a circle?

Back

C = πd or C = 2πr, where C is circumference, d is diameter, and r is radius.

Front

What is the value of π (pi) approximately?

Back

π is approximately 3.14.

Front

If a circle has a diameter of 40 inches, what is its radius?

Back

The radius is 20 inches (radius = diameter/2).

Front

What is the area of a circle formula?

Back

A = πr², where A is area and r is radius.

Front

How do you calculate the circumference of a circle with a radius of 12.5 mm?

Back

C = 2π(12.5) ≈ 78.5 mm.

Front

What is the circumference of a circle with a diameter of 56 m?

Back

C = πd = π(56) ≈ 175.8 m.

Front

What is the area of a circle with a radius of 9 m?

Back

A = π(9)² ≈ 254.34 m².

Front

If the radius of a circle is doubled, how does the circumference change?

Back

The circumference also doubles.

Front

What is the relationship between diameter and radius?

Back

Diameter is twice the radius (d = 2r).

Front

How do you find the area of a circle with a diameter of 10 cm?

Back

First find the radius (5 cm), then A = π(5)² ≈ 78.5 cm².