in measuring the sides of a rectangle, one side is taken 20% in excess and other 10% in deficit. Find the error percent in area calculated.

Area is l*b and any change in respective proportions will directly impact the area.
Use the successive percentage concept, a+b + ab/100
a=20, b= -10,
So 20 - 10 - 2 = 8

Else, use fractions, 20% means 6/5 and -10% means 9/10. Multiplying, we get 54/50 or 108/100
Hence, 8% is the Ans.

8%