A circular ground whose diameter is 70 metres, has a 2.8 metre-broad garden around it. What is the area of the garden in square metres?  Choose the correct choice from the following answers.
A) 540.72 B) 740.64 C) 640.64 D) 620.45 E) 725.26
Req. area = Ï€[(37.8)2 â€“ (35)2]   = 22â„7 Ã— (72.8 Ã— 2.8)[since a2 - b2 = (a + b)(a - b)]   = 22 Ã— 72.8Ã— 0.4 = 640.64 sq m   Answer 640.64
<result>C</result>
A circular ground whose diameter is 70 metres, has a 2.8 metre-broad garden around it. What is the area of the garden in square metres?