I was thinking of buying a Casio Prizm for math, but I found that it didn't have a Computer Algerba System in the already paid for Nspire CAS (firmware ver 2.1). A computer Algebra System can manipulate variables,
Prizm even costs twice as much as a Nspire CAS! Unless you take a SAT/ACT test in College where a Prizm is legit, upgrade to a Nspire CAS over TI-89 Titanium. I think an ordinary $40 B&W Nspire with firmware 2.1 has more math formulas than Prizm right now.