LOGICAL THINKING X

From Reader's Digest

Mary said, "The day before yesterday I was 17. Next year I will be 20." is Mary telling the truth?

Answer:

Yes, but only under very specific conditions. Mary's birthday must be Dec. 31, and she must be saying this on January 1.  Let's say her 18th birthday is December 31, 1995. On January 1, 1996 she correctly said that the day before yesterday (Dec. 30, 1995) she was 17. She was 18 yesterday (her birthday / Dec. 31, 1995 ). On her next birthday (Dec. 31, 1996) she will be 19. Next year she will 20 (on her birthday, December 31, 1997).