Read
about this problem
and many others in "Chance Rules" available below at amazon.co.uk 
QHE Question: This question concerns one of the bestknown probability puzzles 'The Birthday Problem'. How many people should there be in a room so that the probability of at least one of them having the same birthday is fiftyfifty? Choose an interval in which you consider the answer will lie:

Read
about this problem
and many others in "Chance Rules" available below at amazon.com 

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