It’s always amusing to see how few younger people can do arithmetic in their heads. In my current business, we use a lot of basic arithmetic. It cracks me up when I sit in a meeting when the calculators get pulled out for a simple growth or difference calculation. My wife and I used to drill our kids in simple math by making them compete to calculate addition, subtraction, multiplication and division questions in their heads. Our favorite when they were young and still took baths together was to give them rapid fire problems with the loser getting squirted with a squirt gun. It was fun, and they got good pretty quickly!