7th Grade Circumference and Area of Circles Quiz: 10 Questions with Explanations

A 3B 12C 6D 36

The diameter is twice the radius: \(2 \times 6 = 12\).

A \(A = \pi r^2\)B \(A = 2\pi r\)C \(A = \pi d\)D \(A = 2\pi r^2\)

Area uses the square of the radius. \(2\pi r\) and \(\pi d\) are circumference.

A 78.5B 62.8C 31.4D 314

\(C = \pi d = 3.14 \times 10 = 31.4\). The value 78.5 is the area for r = 5.

A \(6\pi\)B \(3\pi\)C \(18\pi\)D \(9\pi\)

\(\pi r^2 = \pi \times 9\). The value 6 pi is the circumference.

A 2B 4C 6.28D 12

\(r = 12.56 \div (2 \times 3.14) = 2\).

A 2B 4C 8D pi

Area depends on the square of the radius, \(2^2 = 4\).

A 50.24B 12.56C 25.12D 100.48

\(r = 4\), whole circle area \(50.24\), half is 25.12.

A 31.4 inchesB 314 inchesC 125.6 inchesD 62.8 inches

One turn equals the circumference: \(3.14 \times 20 = 62.8\).

A \(\frac{7}{22}\)B \(\frac{22}{7}\)C \(2.14\)D \(\frac{31}{4}\)

Pi is about 3.14, and \(\frac{22}{7} = 3.142…\). The other values are too far from 3.14.

A 5 feetB 25 feetC 10 feetD 12.5 feet

\(r^2 = 78.5 \div 3.14 = 25\), so \(r = 5\).