Sara says: "The day before yesterday I was still 14 years old, and next year I shall turn 17." Both of her statements are true. What must today's date and her birthday be?

Let today be 1 January and her birthday 31 December. The day before yesterday was 30 December of the old year, and on that day she was 14. She turned 15 the very next day, on 31 December. So today, 1 January, she is 15; on 31 December of this year she turns 16; and on 31 December of the year after — 'next year' — she turns 17. Both statements hold. The traps: if today were 31 December with a birthday on 1 January, she would turn 15 tomorrow and only 16 next year; a birthday on 2 January gives the same shortfall; and the last option gives up because a jump from 14 to 17 in a few days looks impossible, missing that the two statements straddle two New Year boundaries.