How many odd days are there in the 53 years from 1 January 1901 to 31 December 1953?

Explanation

1. 01

   Leap years in 1901–1953: 1904, 1908, …, 1952, which is 13 years. The other 40 are ordinary.

2. 02

   Odd days $= 13 \times 2 + 40 \times 1 = 66$.

3. 03

   $66 = 9 \times 7 + 3$, so 3 odd days.