I remember being a TA at uni, and taking a practical class on electricity with some first-years, one of the questions involved multiplying 4 by 0.2. One student

I remember being a TA at uni, and taking a practical class on electricity with some first-years, one of the questions involved multiplying 4 by 0.2. One student reached for her calculator and I said "No, you're not allowed to use the calculator for that". She just stared at me like a doe frozen in headlights for a painful 10 seconds until I broke: "Okay, what's 4 by 2?" => "Ooohhhh". Yes, different people have different aptitudes, but some people simply don't want to engage their brain. It's definitely a multivariate problem...