An urn contains 5 white balls and 4 black balls. If 3 balls are randomly selected ( at once, without replacement ), what is the probability that at least 1 ball is black? Give answer as a decimal number with three correct decimal places.
first find prob that they are all white
= (5/9)(4/8)(3/7) = 5/42
so prob that at least one is black
= 1 - 5/42
= 37/42 = .881