We know that, 

Probability of occurrence of an event 

  = \(\frac{Total\,no.of\,Desired\,outcomes}{Total\,no.of\,outcomes}\) 

An ordinary year has 365 days i.e. it has 52 weeks + 1 day. So, there will be 52 Tuesdays for sure(because every week has 1 Tuesday) 

So, we want another Tuesday that to from that 1 day left(as there is only one Tuesday left after 52 weeks) 

This one day can be, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday. Of these total 7 outcomes, the desired outcome is 1, i.e. Tuesday 

Therefore, the probability of getting 52 Tuesdays in an ordinary year =  \(\frac{1}{7}\)

Conclusion: Probability of getting 53 Tuesdays in an ordinary year is \(\frac{1}{7}\)