Question

A park is in the form of rectangle 120m × 100m. At the centre of park there is a circular lawn. The area of park excluding lawn is 8700m2. Find the radius of circular lawn.

Answer 1

Dimensions of rectangular park length = 120m

Breadth = 100m

Area of park = l × b

= 120 × 100 = 12000𝑚².

𝐿𝑒𝑡 𝑟𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑟 𝑙𝑎𝑤𝑛 𝑏𝑒 𝑟

Area of circular lawn = 𝜋𝑟²

Area of remaining park excluding lawn = (area of park) – (area of circular lawn)

⇒ 8700 = 12000 – 𝜋r²

⇒ 𝜋r² = 12000 – 8700 = 3300

⇒`22/7× r^2 = 3300`

⇒ `r^2` = 150 × 7 = 1050

⇒ `r = sqrt(1050) = 5sqrt(42)` 𝑚𝑒𝑡𝑟𝑒𝑠

∴ radius of circular lawn = 5`sqrt(42)` metres.