cool math: lattice multiplication

we stumbled upon lattice multiplication at
it’s a fun and absorbing way for radianceGirl
to simultaneously strengthen her multiplication and addition skills.

take the problem 1,937 x 4,260.
the multiplier, 1,937, goes across the top of the grid
while the multiplicand, 4,260, goes down the right side.
you systematically multiply each number at the end of each column and row,
recording the tens in the upper triangle
and the ones in the lower triangle of each intersection.

for example, when multiplying the 7 in 1937 by 4 in 4260,
one writes the product, 28, by putting the 2 in the upper triangle of the intersection
and the 8 in the lower triangle.

afterward you simply add the numbers along the diagonal
to get your product, 8,251,620.

i can always tell the math is getting good to radianceGirl
when her head is down close to the paper
as she talks herself through the problem.

i wasn’t taught lattice multiplication in school.
what other multiplication algorithms or math concepts are new to you on this go-round?


2 thoughts on “cool math: lattice multiplication

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