2009 AMC 8 Problem 8

The length of a rectangle is increased by 10% and the width is decreased by 10%. What percent of the old area is the new area?

\textbf{(A)}\ 90\qquad\textbf{(B)}\ 99\qquad\textbf{(C)}\ 100\qquad\textbf{(D)}\ 101\qquad\textbf{(E)}\ 110

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.