> but the underlying math is something a 10 year old can handle – as can anyone with a calculator. The calculator is just a tool to get the precision needed. I

> but the underlying math is something a 10 year old can handle – as can anyone with a calculator. The calculator is just a tool to get the precision needed. If you understand the concepts, you can get a rough idea of what '17%' is and whether that ballpark is acceptable. You whip out the calculator only when you need the precision.