Question

The number of rectangles which we can form on a chess board is

• A. $81$
• B. $1296$
• C. $648$
• D. $324$

Answer 1

Answer: (B)

$1296$

Answer 2

There ate 9 horizontal and 9 vertical lines on a chess board. To from a rectangle we require two horizontal and two vertical lines. Thus the no. of rectangles on the chess board $=\,^{9}C_{2} \times \,^{9}C_{2}=36 \times 36$ $=1296$.