Received a question from a reader this morning that will make a nice tutorial.

A box contains 27 black and 3 red balls.Â A random sample of 5 balls is drawn without replacement.Â What is the probability that the sample contains one red ball?

So here’s my thinking and two ways to solve this problem. Instead of red and black balls in an urn type problem, which is pretty abstract, let’s say we know 3 bad parts are in a bin of 30 total parts.