A man wears socks of two colours -black and brown. He has altogether $20$ black socks and $20$ brown socks in a drawer. Supposing he has to take out the socks in the dark, how many socks must he take out to be sure that he has a matching pair?

The correct option is B $3$
If he takes $2$ socks, then it might be black and brown.

If he takes out $3$ socks the,

It can be $2$ black and $1$ brown.

Or it can be $1$ black and $2$ brown.

Either ways he has a choice to wear socks of same color.

Thus, $3$ is correct answer.

Hence, Option B is correct.