Number of days in a leap year =366 days =52 weeks and 2 days
Now 52 weeks contain 52 Sundays and the remaining two days will be one of the
following seven possibilities
(Sun,Mon) (Mon,Tue),(Tue,Wed), (Wed,Thu),(Thu,Fri),(Fri,Sat) and (Sat,Sun)
The probability of 53 Sundays in a leap year is the same as the probability of getting
a Sunday in the above seven possibilities
Required probability is 2/7