Symbiosis National Aptitude Test SNAP 2017 Paper

We can choose 9 squares out of 64 squares in $\stackrel{64}{}{\mathit{C}}_9$ways.
Hence, exhaustive number of cases = $\stackrel{64}{}{\mathit{C}}_9$
From the figure it is clear that the given square of size
3 x 3

can be formed by using four consecutive horizontal and 4 consecutive vertical lines, which can be done in $\stackrel{6}{}{\mathit{C}}_1$ × $\stackrel{6}{}{\mathit{C}}_1$ = 36 ways
Basically you can make 6 squares of size 3 x 3 in vertical direction and 6 squares of the size 3 x 3 in horizontal direction, Hence total 6 x 6 = 36 squares can be chosen.
∴ The required probability
= $\frac{36}{\stackrel{64}{}{\mathit{C}}_9}$