Here’s an example from the maintenance committee for our housing coop. Basically, our budget was off by thousands of dollars, and we were trying to figure out why. The explanation is below in the screen-shot I took of our email exchange.
"What a difference a dot makes."
Finding examples for using mathematics in the real world is this easy. We should find more examples like this one. Imagine you gave the spreadsheet to students (in paper form or otherwise) and said, "Okay, you find the error," and see what the kids come up with.