Discussion on:

Anatomy of an Excel formula: Using functions to perform calculations

The text
If you read this literally (A1 : D1, for example), it reads "the contents of every cell between A1 and B1, inclusive of A1 and B1".
should read
If you read this literally (A1 : D1, for example), it reads "the contents of every cell between A1 and D1, inclusive of A1 and D1".

In Figure G and accompanying text, the formula should reference the C column instead of D.

Listen brother man, have you ever heard of spell check? Cause, you forgot to space many times. Just sayin, because of your job title, I think you know where a spell check button is. xD
P.S. I'monlyinhighschool. Whoops! What I meant to say was
I'm only in high school. I know where spell check is!