Here are some ideas that you might use
To generate random birthdays for groups of 50 people - look at randi, ignoring leap years birthdays are numbers between 1 and 365
For each random sample group of 50 people you can use histcounts with 365 bins to count how many people have each birthday
with result of histcounts, you can determine if the sample has three or more people with the same birthday by taking the max and seeing if it is greater than or equal 3
do this N times and then estimate the probability as the number of times that you have 3 or more people with same birthday divided by N
