largely a substitution exercise

involving trial and perseverance, with some thought maybe

script:

"I'm thinking of a number and you don't know what it is (or do you...?)

here it is [write b]

whatever it is, I'll multiply it by 2 [put a 2 in front of the b]

then I'll add 5 to that

then I'll divide all this by 3 [maybe emphasise by drawing the line slowly, making sure that students are looking at the board]

what does this expression say happened to my number?

OK, all of this here [putting a hand over the expression] is 9

so what was my number?

good, now I'm interested in what other positive whole numbers that this expression could be..."

find a general form for the letters

possibly explaining why these work

what happens for the last one?

and why

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