This Riddle Is Given at High School Math Competitions and It's Tricky as Hell

Cheryl’s list repeats every day except the 18th and the 19th, which eliminates two of the dates from consideration – June 18 and May 19. If she had whispered 18 or 19 into Bernard’s ear, he would have known the whole answer right away, so it can’t be those – a fact he telegraphed to Albert when he says he “didn’t know originally.”

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If Cheryl had told Albert either June and May, he would not be able to say for sure that Bernard couldn’t know the answer. Therefore, June and May are now no longer options for Bernard, leaving him 5 possibilities: July 14, July 16, August 14, August 15, and August 17.

Photo Credit: Pixabay

When Bernard says “I didn’t know originally, but now I do”, Albert can take away any repeated dates (July 14 and August 14), because Bernard would not be able to know if there are two potential answers.

This leaves three possibly dates: July 16, August 15, and August 17.

Since Albert only knows the month, and he claims “Well, now I know too!,” we can again eliminate duplicates here (in this case, August), which leaves the answer: July 16.