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Probability problem?
A boy mentions that none of the 21 kids in his 3rd grade class has had a birthday since school started 56 days previously. Assume that kids in the class are drawn from a population whose birthdays have the same probability on all days of the year. What is the probability that 21 kids would not yet have a birthday in 56 days?
2 respuestas
- LeonardLv 7hace 7 años
assuming 365 days in a year (ignoring leap year Feb 29), prob. of someone having a birthday in one
of the 56 days is 56/365=.1534; so prob. of not having a birthday in one of these 56 days is 1-.1534=.8466.
Prob. of none of the 21 kids having a birthday in these 56 days is (.8466)^21=.0303.
Note: If you used 366 days in the year, you will get a prob of .0306.
