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  • 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]

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