Challenge Problem
A guy from work sent me this riddle today. I'll post what I think is the answer in the comments. Let me know if you think differently and why.
Albert and Bernard just met Cheryl. "When is 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?
6 comments:
July 16.
For Albert to know that Bernard didn't know after Cheryl told them the month and day respectively, that means that she told Albert a month that did not have a unique day. Since 18 and 19 are only seen once in the list, that means that Cheryl didn't tell Albert May or June because they are the months with unique days. That narrows it down to July or August.
Knowing it must be July or August, the only way Bernard can then know the month is if his day is now unique in July or August. 14 is common between the two months, so that leaves July 16, August 15, or August 17 left. Since July 16 is the only choice in July, that's how Bernard knows when Cheryl's birthday is. If Cheryl had told him 15 or 17, he still wouldn't be sure. Using this same logic, now Albert also knows when Cheryl's birthday is.
"All the Federales say, I could have had him any day........"
I can barely wrap my brain around this after reading your solution! Now try this:
1+1+1+1+1
1+1+1+1+1
1+1+1x0+1 =??
Mom says 13
Could you tell the "Federales" post was me?
I figured it was you or Jeddles.
I say 13 as well. Order of operations and all that.
How about 3? Only the bottom line has = and there is no connector between the lines! Never found an official answer.
And it was I who did the anon post without ID.
~Eva
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