Are you kidding are you sure you want this
(3a-4b)²
= 9a² - 12ab + 16b²
There is a chance of 1/16*1/15 that she gets the specific socks pair according to laws of probability and the counting principle but thats not how it will work over here.
As we should be guaranteed that she gets the number of socks she obviously must take out around 9 socks as we are taking the worst case scenario where all the socks that come out are the different ones so the ninth sock must match any of the others.
But if we draw three socks obviously the probability is 1/16*1/15*13/14 as we dont want the third one to be same. We can multiply the answer by 3 as it can be in three different orders.
