Two small squares on a chess board are chosen at random. Probability that they have a common side is,

1/18

There are 64 small squares on a chessboard.

$\Rightarrow$ Total number of ways to choose two squares $={ }^{64}C_2 = 32.63$

For favourable ways we must chosen two consecutive small squares for any row or any columns

$\Rightarrow$ Number of favorable ways $=(7.8) 2$

$\Rightarrow$ Required probability $=\frac{7.8 .2}{32.63}=\frac{1}{18}$