In a leap year we have 366 days. So everyday of a week comes 52 times in 364 days.

Now we have 2 days remaining.

These 2 days can be-

S = {MT, TW, WTh, ThF, FSa, SaSu, SuM}

Where S is the sample space.

As there are total 7 possibilities.

∴ n(S) = 7

Let A denote the event of getting 53 Fridays and B denote event of getting 53 Saturdays.

We have to find P(A ∪ B)

Clearly,

P(A) = 2/7

P(B) = 2/7

And P(A ∩ B) = 1/7

∴ P(A ∪ B) = 2/7 + 2/7 – 1/7 = 3/7