Question

You have a cupboard with a,b,c pairs of red, green and blue socks respectively. you can take out only 1 sock at a time, without looking. find the maximum number of times t you must take out a sock till you get n matching pairs, of any colour. (

Answer 1

if a drawer contains 12 red socks, 16 blue socks, and 20 white socks, how many must you pull out to be sure of having a matching pair?

so the answer is 4. I myself get 5. What am I doing wrong? How would you get 4 as the answer? is there a formula I can use for this question?