December 9, 2001 is Sunday. What was the day on December 9, 1971?

Answer: Option D

We know every year has 1 odd days
We know leap year has 2 odd days
Here, Number of Normal years= 22 and number of Leap years =8
So odd days =22+16 =38 i.e 3 odd days (remainder when 38 is divided by 7,i.e. 3)

Hence, it was a Thursday.