This! I'm horrible at mental arithmetics and I have a degree in engineering. Everyone has access to a calculator in their pocket anyway, and ... Who's going to

This! I'm horrible at mental arithmetics and I have a degree in engineering. Everyone has access to a calculator in their pocket anyway, and ... Who's going to pay with cash within a couple of years? To add to what you said: I think explaining basic concepts is the way to go: Explain compound interest, how much 1$ today will be worth in their retirement at a fixed rate. How does money devalue with inflation, and other basic personal finance aspects. But above all, give people the intuition rather than just say "you should invest your savings"