median
don steward
mathematics teaching 10 ~ 16

Saturday, 12 February 2011

two digadds making 200

place any four digits in the cells
read the two 2-digit numbers across and add them
read the two 2-digit numbers down and add them
then add these two totals together
you are trying to get a target of 200

Students might notice that all the solutions sum to 19
they can also explore this algebraically:
20a + 11(b + c) + 2d = 200
when a = 8, (b + c) can only be 2 and d = 9
when a = 7, (b + c) can only be 4 and d = 8
and so on...

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