Question

Which of the following days cannot be the last day of a century?

• A. Monday
• B. Wednesday
• C. Saturday
• D. Friday
• E. Sunday

Answer 1

The correct option is C

Saturday

100 years contain 5 odd days.

$\therefore$Last day of 1${}^{st}$ century is Friday.

200 years contain (5 $\times$ 2) $\equiv$ 3 odd days

$\therefore$ Last day of 2${}^{nd}$ century is Wednesday.

300 years contain (5 $\times$ 3) = 15 $\equiv$ 1 odd day

$\therefore$ Last day of 3${}^{rd}$ century is Monday.

400 years contain 0 odd days.

$\therefore$ Last day of 4${}^{th}$ century is Sunday.

This cycle is repeated.

$\therefore$ Last day of a century cannot be Tuesday, Thursday or Saturday.