posted by Anonymous .
A box contains 55 balls numbered from 1 to 55. If 15 balls are drawn with replacement, what is the probability that at least two of them have the same number?
take prob that they are both different
first can be anything, the second must be one of the other 54
prob that they are both different = (1)(54/55) = 54/55
prob( they are NOT both different)
= prob(at least two are the same) = 1 - 54/55 = 1/55