A man walking at the speed of 4 km/hr,cross a square field diagonally in 3 minutes.The area of the field is?

Answer: Option A

Speed of man,
= 4 kmph = $$\frac{4\times 5}{18}$$ m/sec
In 3 min (180 sec) man will go = $$\frac{20\times 180}{8}$$ = 200 m.
That means the diagonal of the square field = 200 m.
Diagonal of square,
= Side of Square × $$\sqrt{2}$$  = 200 m.
→ Side of Square = $$\frac{200}{\sqrt{2}}$$
Area of Square = Side²
Area = $$\frac{200\times 200}{2}$$   = 20000 sqm.