Back when video stores still existed our local store had about 5 customers in it when the power went off in the town. The girl behind the counter, a recent HS graduate of about 18, was having trouble figuring out change so all of us old timers would tell her what the change should be. She insisted in laboriously figuring it out on her own. She couldn’t understand how we could figure it in our heads while she could barely get it done with pencil and paper. I told her, “Because we were taught math in school and you weren’t, blame your teachers and government schools”. She didn’t like that answer but the other customers agreed with me.
Back in the old days...1970’s - AKA the pre pocket calculator era... I had a strict math teacher. She said if you can’t do arithmetic in your head, you will get ripped off at the checkout counter. Always calculate the total when adding items to your shopping cart so at least you’d know what you should pay.