what is the probability that 2 of the next 3 American idols will have been born on Sunday?
Assume equal probabilites for being born on any given day of the week. That probability is 1/7. The problem becomes that of having births on Sunday twice and "any other day" once. For each possible sequence of three days,
(Sunday, Sunday, Other)
(Sunday, Other, Sunday)
(Other, Sunday, Sunday)
the probability is
(1/7)^2*(6/7) = 6/343
The "other day" can be the first, second or third of the three, so the total probability is 18/343 = 0.05248