Since the 365 days of the year have 52 weeks
that means that the year have 52 mondays
so the chance in 365 days of being a monday is
52/365
and
52/365= 1/7
then the answer is 1/7
other way of looking at this problem is by thinking that every day of the week have the same change of being celebrete on new year
since we have 7 days in a week, that represents a chance of
1/7