If you like brainteasers, then you're in for a treat with this one.
The puzzle has circulated online amid claims that it originates at no less a prestigious institution than Harvard University.
While these claims have not been confirmed, a copy of the brainteaser handwritten on paper bearing the institution's logo has left people scratching their heads.
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But there's one particular reason why this puzzle is such a tricky one, and it's not because the maths is difficult.
This part of it is just a simple bit of multiplication, but there's another factor which makes the meaning of the brainteaser far more ambiguous.
But before we get into this, let's take a look at the actual puzzle itself, which claims that '90 percent were eliminated'.
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It says: "Seven men have seven wives. Each man and each wife have seven children.
"Q: What's the total number of people?"
Taking a moment to acknowledge the slightly sexist trope of the men being men and the women just being 'wives', you can try to solve it.
Did you solve it?
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There are two ways that you could take this depending on how you interpret the phrasing.
The first one is to interpret the first sentence 'seven men have seven wives' as meaning that the seven men each have seven wives.
So that would be a total of 49 wives and seven husbands, for a total of 56 people.
Then we add in the children, which would be seven for each marriage, so 49 times seven, which is 343 children.
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Adding our 49 wives and seven husbands, this brings us to a total of 399 people.
But there's just one problem - the first sentence doesn't actually specify that the men have seven wives each.
The sentence could describe more of a Seven Brides for Seven Brothers type scenario, with seven men and seven women making up seven married couples.
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This would mean that there are 14 people implied in the first sentence, and the seven couples each have seven children.
So that would be a total of 49 children, and when you add the 14 parents that brings us to a total of 63 people.
While you could theoretically do both given the phrasing of that first sentence, not to mention the fact that bigamy is illegal in most countries around the world, it seems more likely that the second answer is the correct one.
Topics: Education