The perimeter of a semicircle is 25.7 kilometres. What is the semicircle's radius?

The perimeter of a semicircle is given by the formula P = πr + 2r, where r is the radius of the semicircle.

Given that the perimeter P is 25.7 kilometres, we can set up the equation:

25.7 = πr + 2r

To solve for r, we first combine like terms:

25.7 = r(π + 2)

Then, we divide both sides by (π + 2) to isolate r:

r = 25.7 / (π + 2)

Using the approximation π ≈ 3.14, we find:

r ≈ 25.7 / (3.14 + 2) ≈ 25.7 / 5.14 ≈ 5 kilometres

So, the radius of the semicircle is approximately 5 kilometres.