The diagram shows a semi-circle inside a rectangle of length 120 m - OCR - GCSE Maths - Question 6 - 2017 - Paper 1

The curved part of the perimeter is half the circumference of the full circle. The formula for the circumference (C) of a circle is: $C = 2\pi r$ Thus, the curved length (L) becomes: $L = \frac{1}{2} \times 2\pi r = \pi r$
Substituting the radius: $L = \pi \times 60 \approx 188.496 \text{ m}$

The straight edges are the two lengths of the rectangle that are not part of the semi-circle. Each length measures 30 m (since the total length is 120 m) and there are two such edges: So the total length of the straight edges is: $2 \times 30 = 60 \text{ m}$

The total perimeter of the shaded region is the sum of the curved part and the straight edges: $P = L + \text{Straight Edges} = 188.496 + 60 = 248.496 \text{ m}$ Rounding this value to three significant figures gives: $P \approx 248 \text{ m}$