Hint: Perimeter of any shape is equal to the length around the shape.
Complete step-by-step answer:
Given that a field is in rectangular shape with dimensions 50m $ \times $ 40m
$ \Rightarrow $ length = 50m and breadth 40m.
The rectangular field is similar to the below figure.
We know that the perimeter of any rectangle is equal to the sum of measurements of all sides.
$ \Rightarrow $ Perimeter of the given rectangular field = 40 + 50 + 40 + 50 = 180m
The distance covered by a person when he runs around that field = perimeter of field = 180m
Ramesh goes around the field 20 times. That means he covered the perimeter 20 times.
$\therefore $ Distance covered by Ramesh = $20 \times 180 = 3600m$
Note: When a surface is in rectangular shape with length ‘l’ and breadth ‘b’, then perimeter = 2(l + b). We can directly use this formula to calculate the perimeter of the rectangle.