The numeral system of the Mycenaeans is called Aegean numbers. It's an additive system, like almost all numeral systems back then (the later Attic and Ionic numeral systems used by the Greeks were also additive ones). There was no need for zero in such a system. Athena tries to introduce a positional system (like the Hindu-Arabic numeral system that we use today) which is in general more easy to use. Of course they don't understand a thing and begin to suspect that maybe she's a bit nuts (except for Pallas who just thinks it's hilarious that an adult does things that she's not supposed to do).
athena is the best goddess, i can't explain how much i love her
Actually there was calculation with positional numbers with sort-of zero already in Sumerian time (or was it later, Babylonian? Not sure).
Poor Athena really should not start explaining the zero symbol ahead of the positional system, she should invest some thoughts into her teaching first :)