Each side of a rectangular field is increased by 10%. Then the percentage increase in the area of the field is:

21%

10% =  \(\frac{1}{10}\)

                       Old      :     New

Length                10        :       11

Breadth              10        :       11

------------------------------------------------

Area                  100      :        121

{ Area of Rectangle = Length × Breadth }

Percentage increase of Area = \(\frac{121}{100}\) × 100

= 21%