Class 11: Birthday Problem

 

Discussion

 

What is the probability that everybody in your group of 3 or 4 has a different birthday? 

What is the probability that there is a birthday match in your group of 3 or 4? 

 

What is the probability that there is a birthday match in the class? 

What if we include everyone in the class and their mothers (so double the number of people)? 

 

How many people are needed in order to have at least a 50% probability of a match?

 

What is the probability that someone else in the class has your birthday?

 

Journal Assignment:

1.  Use Excel to fill in a table similar the following.  Use Excel formulas.  Print out the table for the first 50 people to include in your journal. How many people are needed in order to have at least a 50% probability of a match?  A 75% chance of a match?  A 95% chance of a match?  Does this agree with your intuition?

 

Person number

Chance that this person will have a different birthday than anyone above them on the list

Chance that everyone on the list so far has different birthdays

Chance that there is a birthday match on the list so far

1

 

 

 

2

 

 

 

3

 

 

 

 

Homework Assignment will be due on Tuesday, Oct 13: 

On blackboard

 

Announcements

Quiz will be on Thursday, October 8.  It will cover normal distributions and correlation and some probability.   Class will run from 1:00 – 2:15 on Thursday.  Next journal collection will be Thursday, October 15.  It will include 4 assignments:  Car and Goat, Drug Testing (from previous handout), Birthday Problem (today’s handout), and Ideas for Final Project (to be assigned next).