walkitout | (Reply)

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The interchangeability of percentages thing seems utterly obvious to me, but I am sure there are similar math topics that aren't. And it's possible it wasn't obvious to me at A.'s age, but I think it was.

Dad had a great anecdote about my oldest sister coming up with a proof of why multiplication is commutative when she was in primary school: if you have seven rows of eight soldiers in formation, and then the drill sergeant says "Face right!" you suddenly have eight rows of seven soldiers, but you haven't added or taken away any soldiers, so you must have the same number.

I have probably mentioned that I get very cross at multiplication tables that are badly typeset and don't show why we call square numbers "square," nor adequately portray multiplication pairs as equivalent. Especially the multiplication table that was in Pee-Chee folders.