Suppose 61 newly created pairs of jeans are placed in a bin to be checked for quality. Of these, 5 will not be of high enough quality to sell. What is the chance that two pairs of jeans selected will be substandard?
Let's take them out one by one.
The chance of the first one to be substandard is
The chance of the second to be also substandard is
So the chance of both of them being substandard is:
(this is an AND situation, so we MULTIPLY):
The chance of only one to be found substandard is: