Too bad businesses are typically run by dolts who don't have the slightest idea how to interpret the data. I've been in charge of "medical informatics" for a large firm and spent a startling amount of time having to explain the difference between a mean and a median to high-level executives.

Since your're in business school, buy a calculator that is specifically setup to support you in completing the coursework.

I used a TI BA2 when working on my MBA/MHA and it was an excellent fit for the coursework. You won't need the TI89s and other scientific calculators (they're overkill for b-school classes).