It's 1/7. In any year,there're atleast 52 weeks which accounts for 52*7=364 days.Now a non-leap year has 365 days i.e. 1 day extra.For this day possiblities will be {mon ,tue, wed, thu, fri, sat, sun}. Thus total no. Of possibilities are 7,out of which there's one possibility of getting 53 sundays i.e. when the extra day is sunday. read more