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# Someone who understands maths explains Cheryl's birthday

You might remember the brilliant Numberphile YouTube series from their videos on the best way to cut cake, shuffle a pack of cards and win at rock-paper-scissors.

This time they have excelled themselves by explaining the 'Cheryl's birthday' maths problem that has confused the world. You know the one:

Don't get it? Simon Pampena explains it in such a way that anyone can understand:

The way to answer this is to break it down and attack it logically.

Essentially it's like a Sudoku. First you break down the dates, then you break down what Albert - who knows the month - and Bernard - who knows the date - know.

Albert says he does not know when Cheryl's birthday is. But he also knows that Bernard does not know. That means he knows Cheryl didn't whisper May 19 or June 18, which only had one option for a date, to Bernard - so she can't have given either of those months to Albert.

That leaves us five options:

For Bernard to know the birthday he already has the date. He just needs the month. So from what Albert has said, Bernard is able to say what the month is.

That leaves Albert three options. It could have been July 16, August 15 and August 17.

Albert then says he also knows when Cheryl's birthday is. Given that he only knows the month and that there are two options left in August, that means Cheryl's birthday must be on July 16. And there you have it.

See the full explanation below:

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