If each side of rectangle is decreased by 11%, then its area will decrease by:

let the length of rectangle=10L and breath= 10B

area of rectangle=10L*10B=100LB

after decrease in each side the area of rectangle=8.9L*8.9B=79.21L

percentage change in area of a rectangle=  $$\frac{change  in  area}{original  area}$$*100

                                                                  = $$\frac{100LB-79.21LB}{100LB}$$*100

                                                                  =20.79%

alternate method:

we can use successive percentage formula.

percentage change in area of a rectangle=a+b-$$\frac{ab}{100}$$

                                                                  =11+11-$$\frac{11*11}{100}$$

                                                                  = 22-1.21=20.79%