Clue to Puzzle #45: If one child is a boy, what is the probability the other is a boy?
45. A lady has two children. One is a boy. What are the chances of the other child also being a boy?
How does this change if you are told the oldest child is a boy?
How does this change if you are told the oldest child is a boy?
I think we can reasonably assume that since this is a riddle or a puzzle the answer is unlikely to be 50%. In terms of a clue, it's noteworthy that the question doesn't say only one child is a boy, 'a child is a boy' could equally have been written as at least one child is a boy.
From there you need to think about the combinations of boys and girls, how many there are, how many meet the criteria at least one boy and then finally how many of them meet the criteria that the other child is a boy.
It may bee too much of a clue, but I have done that below. The table below shows the possible gender combinations of two children.
Where next?
Questions Answer
From there you need to think about the combinations of boys and girls, how many there are, how many meet the criteria at least one boy and then finally how many of them meet the criteria that the other child is a boy.
It may bee too much of a clue, but I have done that below. The table below shows the possible gender combinations of two children.
Where next?
Questions Answer
© Nigel Coldwell 2004 - – The questions on this site may be reproduced without further permission, I do not claim copyright over them. The answers are mine and may not be reproduced without my expressed prior consent. Please inquire using the link at the top of the page. Secure version of this page.
PayPal
I always think it's arrogant to add a donate button, but it has been requested. If I help you get a job though, you could buy me a pint! - nigel
