Chance of at least two were born on the same day of the week = 1 - Chance of all three born on different days of the week
Chance of three random people born on different days of the week = 1 * 6/7 * 5/7 = 30/49
Chance of at least two were born on the same day of the week = 1 - 30/49 = 19/49
Sorry for re-post, didn't see the above reply
I believe this is also called the birthday paradox. Birthday problem - Wikipedia, the free encyclopedia