Supposing 30 days in the month of May (which is not always same in every year),we have,
S= Sample Space
n(S)=total days in a year=365 days
n(E)=no of favourable events
= no of days in the month of May=30 days
Then the probability is of favourable events is,
P(E)=n(E)/n(S)=30/365=6/73
Now,the probability that the birthday is not in May is,
P'(E) =1-6/73=67/73 ANS!!!