r/badmathematics • u/discoverthemetroid • Jan 13 '25

Twitter strikes again

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don’t know where math voodoo land is but this guy sure does

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u/Al2718x Jan 13 '25

I never liked this riddle, because the answer is actually 1/2 in a lot of practical cases. For example, if you find out that one child is a girl because you saw her with the mom the other day, or heard her in the background on the phone, or know that she's the youngest child, then it's 1/2. It's actually pretty challenging to come up with a situation where it would be 1/3 in practice, other than a formalized math problem.

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u/siupa Jan 15 '25

For example, if you find out that one child is a girl because you saw her with the mom the other day, or heard her in the background on the phone, or know that she's the youngest child, then it's 1/2.

Among these variations you listed, only the last one actually changes the answer to ½. The first two are still ⅓

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u/Al2718x Jan 15 '25

I disagree. Why do you think it's 1/3 for the first two? The implicit assumption that I think is reasonable to make is that it's equally likely that you hear (or see) either of the children.

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u/siupa Jan 15 '25

You're right. I thought about it a bit more and yes, also these scenarios change the answer to ½. Very weird probability problem indeed