An error of 2% in excess is made while measuring the side of a square. The percentage of error in the calculated area of the square is

100 cm is read as 102 cm

a = 100 x 100 sq.cm and b = 102 x 102 sq.cm

then, Increase in area = [ (102 x 102) - (100 x 100) ] sq.cm

percentage error = $\frac{404}{100*100}*100$= 4.04%