Calculating Areas and Circumferences of Circles

Front

What is the formula for calculating the area of a circle?

Back

Area = π × r², where r is the radius.

Front

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

Back

π is commonly approximated as 3.14.

Front

What is the formula for calculating the circumference of a circle?

Back

Circumference = 2 × π × r or Circumference = π × d, where d is the diameter.

Front

If a circle has a radius of 5 feet, what is its area?

Back

Area = π × (5)² = 3.14 × 25 = 78.5 square feet.

Front

If a circle has a diameter of 12.5 feet, what is its radius?

Back

Radius = Diameter / 2 = 12.5 / 2 = 6.25 feet.

Front

What is the relationship between radius and diameter?

Back

Diameter = 2 × Radius.

Front

How do you convert diameter to radius?

Back

Divide the diameter by 2.

Front

What is the area of a circle with a diameter of 42 inches?

Back

Area = π × (21)² = 3.14 × 441 = 1385.94 square inches, rounded to 1386.

Front

How much fencing is needed for a circular pond with a diameter of 12.5 feet?

Back

Circumference = π × d = 3.14 × 12.5 = 39.25 feet.

Front

What is the area of a circle with a radius of 10 cm?

Back

Area = π × (10)² = 3.14 × 100 = 314 square cm.