Four Digit Codes
Your grades are displayed using four-digit codes.
Here are the probabilities
that in a class of N students, two students choose the same code.
Notice that once we have about 120 students then there is a better
than 50-50 chance that at least one code will be duplicated.
For sections of 30 students, the probability of duplication is
only about 1 in 23.
These were calculated using a fortran program.
These calculations assume that each choice is equally likely.
This is similar to assuming that each choice of lottery numbers is
equally likely, which is not the case, because people choose numbers
such as birthdays of family members.
The CHANCE
website includes a discussion of
lotteries,
including some interesting statistics.
John Mitchell