What would the perimeter of a 20ft semicircle be?

Answer 1

That depends on what you mean by a "20 ft semicircle".

A semi-circle is a half circle.

A 20 ft circle could be:

• A circle of diameter 20 ft

The perimeter of the semicircle is half the circumference plus the diameter

→ perimeter = 1/2π 20 ft + 20 ft

= 10π + 20 ft

≈ 51.42 ft

• A circle of radius 20 ft

The perimeter of the semicircle is half the circumference plus double the radius

→ perimeter = 1/2 2π 20 ft + 2 x 20 ft

= 20π + 40 ft

≈ 102.08 ft

• A circle of circumference 20 ft

The perimeter of the semicircle is half the circumference plus the diameter

→ perimeter = 1/2 20 ft + 20 ft ÷ π

= 10 ft + 20/π ft

≈ 16.37 ft

However, if a 20 ft circle is a circle with a circumference (= perimeter) of 20 ft then a 20 ft semi-circle could be a semicircle with a perimeter of 20 ft

→ perimeter = 20 ft