Lord B ... you may be in a minority, but I think it's a significant minority. As you so correctly surmise, logic can reign supreme over numerics or alphabetice, but either can be a struggle. I get the impression from posts here and elsewhere that some people do indeed suffer a mind-numbing blank once a quarter, and just step back from the numerical challenge.
For my part, I enjoy these, but despite a couple of good maths A levels, could not get close without assistance from an electronic spreadsheet.
A nice diversion, but I recko that one per quarter is just about right.