It shouldnât 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 wouldnât faze me. Lately, though, I have had the sense that my brain isnât firing on all cylinders. Itâs not just maths, but a general sluggishness. This matters to me.