Question 25
A square piece of graph paper of side length $30\text{ mm}$ contains $900$ smallest squares of side $1\text{ mm}$. Its four rectangular corners $A,B,C,D$, in clockwise order, are cut away. The resulting paper is a cross as shown. Let $N$ be the total number of rectangles, excluding all squares, contained in the resulting paper. Find $N/10$.
