It shouldn’t have been difficult: 72 x 72. From the back seat, my daughter, newly confident in mental maths, wanted to check her answer. Whether it was because it was the end of the day, I was trying to park or something else, I stalled, cognitively speaking. Normally, that sum wouldn’t faze me. Lately, though, I have had the sense that my brain isn’t firing on all cylinders. It’s not just maths, ...