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Cross addition isn’t a thing

stadel proportion


Presented without comment, and with thanks to Andrew.

2 replies on “Cross addition isn’t a thing”

Apparently it is – and it’s much easier than the insanity-producing cross-multiplication. Of course, it’s not a procedure that would give one any answers that meet with any other reality, but it’s still easier. 🙂

I would want to teach this kid to multiply both sides by 30 as the first step in a problem like this — same as solving any other type of equation in which the variable only occurs once, use inverse operations to isolate your variable.

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