Tuesday, April 14, 2015

Logic/illogical question that went viral

Full article was referred here (from AsiaOne).
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The following is the question.
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Albert & Bernard just become friends with Cheryl, & they want to know when her birthday is. Cheryl gives them a list of 10 possible dates
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May-15   May-16   May-19
June-17   June-18
July-14   July-16
August-14   August-15   August-17
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Cheryl then tells Albert & Bernard separately the month & the day of her birthday respectively.
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Albert: I don't know when Cheryl's birthday is, but I know that Bernard does not know too.
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Bernard: At first I don't know when Cheryl's birthday is, but I know now.
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Albert: Then I also know when Cheryl's birthday is.
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So when is Cheryl's birthday?
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=======
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There are ten dates given by Cheryl. Bernard knows the day and Albert knows the month. Are they competing or what? There is no indication for the rule of this game which is frustrating, e.g. no sharing of direct information or what?
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Logic.
If Bernard was given either 19 or 18, he would have shouted I know! But he didn't. So Albert made the first comment about Albert not knowing it.
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June-17 was not it either because Bernard would have shouted I know already if he had deduced that Albert didn't know and if the month he was given was June. So June is out.
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Next is the strangest deduction by Bernard. He claimed he knew the answer, but based on what?
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After striking out the improbable answers. He is left with these.
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May-15   May-16
July-14   July-16
August-14   August-15   August-17
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When Albert said "I know that Bernard does not know too", Bernard SPECULATED that it couldn't be May or June. Why strike out May (and based on what information)?
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That would leave the following.
July-14   July-16
August-14   August-15   August-17
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Bernard secret answer is July-16 (student don't know it yet).
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Then Albert butted in saying he knew too. 
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Albert based his deduction on this, i.e. There are two 14s, so it is unlikely to be that because Bernard can't possibly guess the month. He stroke out the improbables. What are left would be.
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July-16
August-15   August-17
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Albert can't possible guess the days in August (there are two), and that leaves July-16 as the most probable answer for students to guess right.
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Back to the main problem in this question.
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To me, the major problem with this question is its inadequate information. I don't know how many contenders were able to answer this problem but I know I wouldn't be able to get it.
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IMHO, if the mock conversation had been such.
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Albert: I don't know when Cheryl's birthday is, but I know that Bernard does not know too because it doesn't fall on the months where he could have possibly guessed.
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Bernard: At first I don't know when Cheryl's birthday is, but I know now.
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Albert: Then I also know when Cheryl's birthday is.
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With the sentence in bold, then Bernard wouldn't have to speculate that May and June are improbables.
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Educated assumptions is good but speculation is not!
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Just a share.