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## Math for fun and glory

### Course: Math for fun and glory>Unit 2

Lesson 1: Brain teasers

# Cheryl's birthday

Deductive reasoning problem from Singapore.

## Want to join the conversation?

• Can you please make it more clear because I didn't understand how it became July 16?
• Sorry, but June 16th was not even in the question. The answer is June 18th.
• Why doesn't Cheryl just tell them her birthday instead of making them have a hard time guessing. Or why don't Albert and Bernard just share their information to figure out the month and day of her birthday. Isn't it simpler that way?
• Cheryl wants to give Albert and Bernard a challenge. What would be the point of giving them a problem if she is just going to give them the answer?
• In the top left corner, there is a 24.
Are there any other Deductive reasoning problems that Sal was given?
• The 24 represents that it was problem number 24 on a math test. The other questions were not based in pure logic.
• How do you know when you do the teaser that Albert knows that its not May or June?
• Since Cheryl only gave just one number of the day for May, and just one for June, if Bernard was given the month, he would already know her birtday, but Albert says that Bernard doesn't know when her birtday is
• At the end of the video, Bernard's list still has months to cross off, and did not reach a conclusion. How then does Bernard know Cheryl's birthday
• If Albert & Bernard are trying to determine the solution without giving each other any clues, why would they respond the way they did above and give each other the answer? If they were trying to determine the answer together, why didn't they just share what they knew?
• They were able to share what they knew, just indirectly. Since we know they're good logicians, and as friends they know they're both good logicians, they would probably know that the other would be capable of figuring out the answer based off of the indirect hints they give. Who says they can't challenge each other? =)
(1 vote)
• How can Albert find out that the birthday is not on May 15th or 16th? I don't see how "i know that he does not know" implies that the month is not May. The fact that he only knows the date and not the month means that the day numbers that only exist once (i.e 19 May and 18 June ) are not her birthday days. I can't see how this fact correlates with her birthday not being in May. There are two more days in May for which Bernard has no information whatsoever.

My train of thought was the following :
-Albert knows that Bernard knows only the day.
-They both know all the possible birthdays.
-So Albert can take out all the day numbers that exist once because he knows that Bernard does not know.
-Then he can take out June because he knows the month and it has only 1 date, therefore if it was June he would know the birthday date.
-? ? ?
(1 vote)
• Albert can eliminate the months of May and June because he was told what month it was, and that month is not May or June. The reason we can eliminate May is because Albert says that he knows Bernard does not know. Albert knows that Bernard doesn't know because Albert must have been given a month that doesn't include a day number that exists only once.
• I try to solve it myself but I don't know what to do and I don't know how you guess the numbers....
• Brain teaser based on Korean drama show My Daughter Geum Sa Wol:
So Kook-Ja (Grandma Emiko) baked 2 batches of Bum Bum Emiko Cookies.
They were both for her granddaughters. There was a batch of rainbow sprinkled cookies and a batch of chocolate chip cookies. Which batch was for Dalleh? Which batch was for Jjilleh?
Hints:
Both granddaughters love the colors of the rainbow.
The girls both have sweet tooths.
Be sure to watch My Daughter Geum Sa Wol TODAY from PM to PM!
(1 vote)