Brain Teasers · Albert, Bernard and the Birthday
Cheryl's Birthday Puzzle - Play It and Check July 16
Cheryl's birthday puzzle: one knows the month, one knows the day, and three sentences give the date away.
What is Cheryl's birthday puzzle?
It is a puzzle about knowledge: each statement tells you something about what one person could or couldn't have known, and that rules dates out.
The hard step is 'I know that you don't know', which is a statement about the other person's possible information.
How it works
Ten possible dates. Albert is told the month and Bernard the day. Albert says he doesn't know but knows Bernard doesn't either. Bernard says he now knows. Albert says he knows too. The story asks for the date. You type your answer and check it. Then you step through the answer and the breakdown.
How scoring works
This teaser checks your answer. Any correct form counts - a fraction, a decimal rounded correctly, a percent, or the number in words. You get two tries before the answer opens. A correct first try earns a ticket; a second try or opening the answer early is recorded but earns nothing. The story teasers share one lifetime unlock for free users.
The key insight
Days 18 and 19 appear once, so Albert's month is neither May nor June. Of July 14, 16 and August 14, 15, 17, Bernard now knows, so the day isn't 14. Of July 16, August 15 and 17, Albert knows, so it is July: July 16.
The full step-by-step solution lives at /brain-teasers/cheryls-birthday/solution.
A worked example
Strike May and June, then the two 14s, then August. One date is left: July 16.
Common mistakes
• Answering August 17 by misreading the last statement.
• Ruling out only May 19 and June 18, not their whole months.
• Trying to hold the list in your head instead of striking dates out.
Why interviews test this
Interviewers use it to see whether you can reason about what someone else knows, one statement at a time. The written solution is at /brain-teasers/cheryls-birthday/solution.
Play Albert, Bernard and the Birthday on Outcry
Albert, Bernard and the Birthday is free to play on Outcry, in the Brain Teasers section, and every run is timed and scored. Read the guide once, then play Albert, Bernard and the Birthday and check your score against the strategy above. The guide book has a written guide for every other game, and the practice hub and mock assessments put the same skills under a real screen's clock.