Area and circumference 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

If the diameter of a circle is 9 feet, what is the radius?

Back

Radius = Diameter / 2 = 9 feet / 2 = 4.5 feet.

Front

What is the value of π (pi) commonly approximated as?

Back

π is commonly approximated as 3.14.

Front

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

Back

C = 2πr = 2 * 3.14 * 12.5 mm = 78.5 mm.

Front

If a circle has a circumference of 62.8 inches, how do you find the radius?

Back

Use the formula C = 2πr. Rearranging gives r = C / (2π) = 62.8 inches / (2 * 3.14) = 10 inches.

Front

What is the relationship between diameter and radius?

Back

The diameter is twice the radius: Diameter = 2 * Radius.

Front

If a bike tire has a radius of 1.5 feet, how far does it travel in 3 rotations?

Back

Distance = Circumference * Number of Rotations = (2πr) * 3 = (2 * 3.14 * 1.5) * 3 = about 28 feet.

Front

What is the circumference of a circle with a diameter of 14 inches?

Back

C = πd = 3.14 * 14 inches = 43.96 inches.

Front

How do you convert diameter to radius?

Back

Divide the diameter by 2.

Front

What is the circumference of a circle with a radius of 5 cm?

Back

C = 2πr = 2 * 3.14 * 5 cm = 31.4 cm.