Archive | April 2015

Birthday Puzzle

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My class openers are getting to be my favorite part of a lot of my classes this year.  (Huge thanks to Andrew and Fawn for their part in that.  I need to do another post on how I use those two excellent resources.)  After seeing this article in the Times last night, I put the following puzzle to my students as our class opener today.

Albert and Bernard just met Cheryl.  “When’s your birthday?” Albert asked Cheryl.

Cheryl thought a second and said, “I’m not going to tell you, but I’ll give you some clues.”  She wrote down a list of 10 dates:

May 15               May 16            May 19
June 17              June 18
July 14               July 16
August 14         August 15        August 17

“My birthday is one of these,” she said.  Then Cheryl whispered in Albert’s ear the month — and only the month — of her birthday. To Bernard, she whispered the day, and only the day.

“Can you figure it out now?” she asked Albert.

Albert: “I don’t know when your birthday is, but I know Bernard doesn’t know, either.”
Bernard: “I didn’t know originally, but now I do.”
Albert: “Well, now I know, too!”

When is Cheryl’s birthday? Read More…