- A normal year has
- 52 Mondays
- 52 Tuesdays
- 52 Wednesdays
- 52 Thursdays
- 52 Fridays
- 52 Saturdays
- 52 Sundays
- + 1 day that could be anything depending upon the year under consideration.
- In addition to this, a leap year has an extra day which might be a Monday or Tuesday or Wednesday or Sunday.
Our sample space is S : {Monday-Tuesday, Tuesday-Wednesday, Wednesday-Thursday,..., Sunday-Monday}
Number of elements in S = n(S) = 7
What we want is a set A (say) that comprises of the elements Saturday-Sunday and Sunday-Monday i.e. A : {Saturday-Sunday, Sunday-Monday}
Number of elements in set A = n(A) = 2
By definition, probability of occurrence of A = n(A)/n(S) = 2/7
Therefore, probability that a leap year has 53 Sundays is 2/7.
(Note that this is true for any day of the week, not just Sunday)
[via Brainly]
