### Home > INT3 > Chapter 10 > Lesson 10.3.1 > Problem 10-144

FINDING BIRTHDAY TWINS

If you randomly select a group of just 21 people the chance of there being a pair of people with the same birthday is greater than 50%. This surprising fact is due to the large number of pairings possible in a group of 21 people. Homework Help ✎

Determine the number of possible unique pairings in a group of 21 people.

Compute the probability that any given pair of people have the same birthday (ignoring leap day).

Compute the probability that any given pair of people

*do not*have the same birthday (ignoring leap day).Now compute the probability that exactly one pair out of the 21 people has the same birthday.

Unique pairings refer to the number of combinations of 2.

See part (b).

Use the answers from parts (a) – (c) to determine the probability.