If there are 9 horizontal lines and 9 vertical lines in a chess board, how many rectangles can be formed in the chess board? Pick.
A) 1452  B) 1243  C) 1564  D) 1296  E) 1234
Number of rectangles that can be formed by using m horizontal lines and n vertical lines   = mC2 × nC2   Here m = 9, n = 9   Hence, number of rectangles that can be formed   = mC2 × nC2   = 9C2 × 9C2 = (9C2)2   =(9×82×1)2=362=1296=(9×82×1)2=362=1296   Ans: 1296
<result>D</result>
If there are 9 horizontal lines and 9 vertical lines in a chess board, how many rectangles can be formed in the chess board?