To calculate the probability that at least two people in a class of 30 share the same birthday, we can use the complement rule, which states that the probability of an event happening is equal to one minus the probability of the event not happening.
If we assume that birthdays are uniformly distributed throughout the year (i.e., each day is equally likely to be someone's birthday), then the probability that no two people in the class share the same birthday is:
365/365 * 364/365 * 363/365 * ... * 336/365
This is because the first person can have any birthday (probability of 365/365), the second person must have a different birthday (probability of 364/365), the third person must have a different birthday than the first two (probability of 363/365), and so on, up to the 30th person, who must have a different birthday than the first 29 (probability of 336/365).
Calculating this probability gives us:
(365/365) * (364/365) * (363/365) * ... * (336/365) ≈ 0.2937
So the probability that no two people in the class share the same birthday is approximately 0.2937.
Using the complement rule, the probability that at least two people in the class share the same birthday is:
1 - 0.2937 = 0.7063
Therefore, the probability that at least two people in a class of 30 share the same birthday is approximately 0.7063, or 70.63%.