Guest Post: Four Ways To Compute A Probability

This guest post by Mr John Chase first appeared here on White Group Mathematics, 10 May 2014

One thing I love about math, and particularly combinatorics and probability, is the fact that many methods exist for solving the same problem.

Each method may have its advantages. The advantage might be conceptual (as in “this makes most sense to me”) or the advantage might be computational (as in “this is the fastest way to do it”).

Discussing the merits of different methods is exactly what math class is for!

For example, check out this typical probability question that could appear in a Precalculus course:

The Texas Ranger pitching staff has 5 right-handers and 8 left-handers. If 2 pitchers are selected at random to warm up, what is the probability that at least one of them is a right-hander?

In fact, it’s one I use in my own Precalculus course and it generated a great class discussion. In teaching it this past year, I ended up showing students four ways to do the problem this year! Here they are:





Have I convinced you that there are lots of good ways to approach this problem? What approach do you like best?

Here’s another question for homework . See if you can do it in all four ways!





About The Author

John Chase is a Math teacher at Richard Montgomery High School in Rockville MD. He is currently getting his masters in Math at Johns Hopkins University, and he blogs at Random Walks.