Suppose a bag contains 4 white chips and 6 black chips. What is the probability of randomly choosing a white chip, not replacing it, and then randomly choosing another white chip?
There are initially
#4/10 = 2/5#
Having drawn a white chip there are then
#3/9 = 1/3#
So the probability of drawing two white chips is:
#2/5 * 1/3 = 2/15#