The last day of a century cannot be
100 years contain 5 odd days.
$\therefore$ Last day of 1st century is Friday.
200 years contain 5 x 2 $\equiv$ 3 odd days.
$\therefore$ Last day of 2nd century is Wednesday.
300 years contain 5 x 3 = 15 $\equiv$ 1 odd day.
$\therefore$ Last day of 3rd century is Monday.
400 years contain 0 odd day.
$\therefore$ Last day of 4th century is Sunday.
This cycle is repeated.
$\therefore$ Last day of a century cannot be Tuesday or Thursday or Saturday.