[pacaro]

I guess that I was taught basic mental arithmetic differently. Multiply by 8 and divide by 5, or (it's inverse) is two single instruction cycle opcodes (or whatever my brains equivalent is).

Regularly needing to translate between sane units and US (and occasional British) idiosyncrasies keeps these mental muscles worked enough that it's mostly subconscious now.

I didn't enjoy rote repetition of times tables and drills as a kid, but it's frustrating seeing my daughter being taught to understand multiplication, and learning "strategies", but struggling with mental arithmetic (I mean she tests above grade level, so I'm not worried, it's just a _get off my lawn_ reflex)

[jameshart]

Arithmetic strategies are great but you still need a bunch of quick operations (like doubling and multiplying by 10) and fundamental lookup tables (like basic multiplication tables, squares, powers of two) to bootstrap them from.

I don’t think knowing all the times tables up to 12 is as helpful as having a good appreciation for how to break a multiplication into simpler parts, but you do need immediate recall on multiples of all the single digit numbers, up to at least times five or six.