2013 Cayley Problem 5

A rectangular field has a length of 20 metres and a width of 5 metres. If its length is increased by 10 m, by how many square metres will its area be increased?

\textbf{(A)}\ 10\quad \textbf{(B)}\ 20\quad \textbf{(C)}\ 50\quad \textbf{(D)}\ 75\quad \textbf{(E)}\ 100

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Cayley contests here.