Birthday Problem: Find the Probability of 3 People Sharing the Same Birthday

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In summary, the probability that three people selected at random will all share the same birthday is 0.00000751, while the probability that none of the three will share the same birthday is 0.992. This calculation assumes 365 days in a year and uses a direct counting approach to determine the number of possibilities for each scenario.
  • #1
skip_it2
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Three people are selected at random. Find the probability that

(a) all three share the same birthday:

(365/365)(1/365)(1/365) = 0.00000751

(b) none of the three shares the same birthday. Assume 365 days in a year.

(365/365)(364/365)(363/365) = 0.992
 
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  • #2
Sorry - I was thinking this was a homework forum problem - is it homework?
Try a direct counting approach:
1) Figure out how many possibilities there are for birthdays for the three (no restrictions)
2) For 'a', count the number of ways all three could have the same birthday, then divide by the answer to '1'
3) For 'b', count the number of ways none have the same birthday, then divide by the answer to '1'

Thanks for adding your work. It wasn't here before.
 
Last edited:
  • #3
Your answers are correct.
 

Related to Birthday Problem: Find the Probability of 3 People Sharing the Same Birthday

1. What is the Birthday Problem?

The Birthday Problem, also known as the Birthday Paradox, is a mathematical problem that calculates the probability of at least two people sharing the same birthday in a group of a certain size.

2. How is the probability of 3 people sharing the same birthday calculated?

The probability of 3 people sharing the same birthday can be calculated by using the formula:
P(n) = 1 - (365!/((365-n)! * 365^n))
where n is the number of people in the group. This formula takes into account the chances of each person having a different birthday and subtracts it from 1 to get the probability of at least two people sharing the same birthday.

3. Is the Birthday Problem applicable in real life situations?

Yes, the Birthday Problem is applicable in real life situations. It is often used in statistics and probability to demonstrate the concept of unlikely events occurring in a group of people.

4. What is the probability of 3 people sharing the same birthday in a group of 23 people?

The probability of 3 people sharing the same birthday in a group of 23 people is approximately 50%. This means that in a group of 23 people, there is a 50% chance that at least two people will share the same birthday.

5. Can the Birthday Problem be extended to more than 3 people?

Yes, the Birthday Problem can be extended to any number of people. The formula used to calculate the probability of 3 people sharing the same birthday can be modified to include more people in the group.

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