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BRAINTEASERS

Can You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into Confusion

Date December 12, 2019

Author By Eliza Carnell

Cheryl's birthday puzzle is one of those math riddles that took the internet by storm when it first came out. Since then, it has popped up every once in a while, daring people to push their minds to find the answer.

See the infamous 8th-grade question below. It was set for Singaporian students aged 14.

You can see why this math problem caught the attention of people and led to a lot of confusion too. Can you give it a try? Oh, and to clear up any confusion about the question, Cheryl only told Albert her birthday month and told Bernard the day.

This means that Albert is either told May, June, July or August. And Bernard is told either 14, 15, 16, 17, 18 or 19. Clear? Now start working it out.

So when is Cheryl's birthday

Even though it doesn't seem like it, this question actually gives us all we need to solve it. If you're struggling, you can figure it out following the train of thought of Alex Bellos, who shared his working with The Guardian.

Can You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into Confusionantoniodiaz / Shutterstock.com

Now the puzzle read:

Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard doesn’t know too.

It makes sense that Albert doesn't know when Cheryl's birthday is. He was only given the month so it could be basically any date. And based on the information too, the only way Bernard will know the correct date with a single number will be if Cheryl had told him either 18 or 19. These are the only dates from the options that appeared once (May 19 and June 18).

Can You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionBojan Milinkov / Shutterstock.com

Since Albert is sure Bernard doesn't know, then that means Albert was told July or August, ruling out the 18 and 19 months that Bernard had.

Are you with us so far? Good!

Can You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionTierneyMJ / Shutterstock.com

So, now that Bernard has figured out it's July or August, then he knows it could be either 15, 16 or 17. If he had been told 14 he still wouldn't know whether the month was August or July. 15, 16 and 17 are only tied to one specific month, but 14 could be either.

Now, the options are either July 16, August 15 and August 17. So for him to know for sure, then he must have been told July. Since if he had been told August, he will not know which date for certain is the birthday.

Can You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into ConfusionCan You Figure Out When Cheryl's Birthday Is? The 8th Grade Math Question That Plunged The Internet Into Confusionmimagephotography / Shutterstock.com

The answer to this puzzle is then July 16.

Funny responses

Figuring out Cheryl's birthday problem became an inspiration for some people to come up with interesting responses.

A few Twitter users took a stab at it and dropped their uniquely hilarious theories.

Truly, when you're stumped, all you can do at first is have a good laugh. But then, there's nothing wrong with giving the puzzle a shot. Even if you don't get it, you still get to push your mind to try and work it out. And that's a fantastic exercise for your brain too.

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