You're walking down the street when a stranger approaches you. The stranger informs you that he has a riddle and will give you $100 if you can solve it. You agree and he follows up with, "I have one daughter who was born on a Friday. What are the odds my second child is also a daughter?". Assume equal odds of a daughter or son being born as well as equal odds of being born on any day of the week.
Comments:
Anonymous - 10 years, 5 months ago
Well.. there is no information about his other children.. so maybe the daughter born on friday is his second child? maybe he only have one?
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Max Burstein - 10 years, 5 months ago
Safe to assume he has 2 children
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Anonymous - 10 years, 5 months ago
Is the $100 offered to make you think the riddle is hard? Unless I'm missing something the odds would be 50%. Gender of the first child is irrelevant and the actual question doesn't take weekday into account.
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Max Burstein - 10 years, 5 months ago
That's definitely one answer. This is actually a rework of the Tuesday Birthday Problem to fit for us on Friday. There are some pretty good write ups on it if you Google it. Some mathematicians argue a different answer, though I like the 50/50 answer.
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mick - 10 years, 5 months ago
50%
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SippieCup - 10 years, 5 months ago
There is a 0% chance that he has another daughter. He has stated he only has a single daughter, who happened to be born on a friday. This means that all other children are sons, as if he had multiple daughters, he would have said I have a daughter who was born on friday, not I have one daughter who was born on friday.
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Karl - 10 years, 5 months ago
Not sure if I agree there - just because he said 'one' instead of 'a' doesn't mean he only has one daughter.
I could say "I have one daughter who was born on Friday. I have another one that was born on Saturday."
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Max Burstein - 10 years, 5 months ago
It is possible he has a second daughter
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Sid - 10 years, 5 months ago
The it is 48%
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Sid - 10 years, 5 months ago
I am also SippieCup. Anyway the reason it is 48% is because the odds of having a boy or girl is 50/50 6 days of the week, however since he only has one daughter born on a saturday that means that if there was another child born on a saturday it is 100% that it is a boy.
Thus, there is a 13/27 chance that the child is a daughter.
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