Three integers are chosen at random without replacement from the first 20 positive integers. What is the probability that their product is even?
For the product to be even there must be at least one even integer.
Probability of no even integers p0 = (10/20)*(9/19)*(8/18)
Hence probability of at least one even integer = probability of even product p = 1 - (10/20)*(9/19)*(8/18)
(Edited to make more sense! Thanks EP).