Given number of socks in the box = 4
Let B and W denote black and white socks respectively. Then we have
S = {B, B, W, W}
If a white sock is picked out, then the total no. of socks left in the box = 3
Number of white socks left = 2 – 1 = 1
Probability of getting white socks = number of white socks left in the box/ total number of socks left in the box
= 1/3