In a leap year the probability of having 53 Sundays or 53 Mondays is

Since a leap year has 366 days and hence 52 weeks and 2 days. The 2 days can be $SM\mathit{,}\mathit{ }MT\mathit{,}\mathit{ }TW\mathit{,}\mathit{ }WTh\mathit{,}\mathit{ }ThF\mathit{,}\mathit{ }FSt\mathit{,}\mathit{ }StS$. Therefore, P(53 Sundays or 53 Mondays)

$=\frac{2}{7}+\frac{2}{7}-\frac{1}{7}=\frac{3}{7}.$