When she started talking about Ninja lines I knew this was blog material. I took step-by-step fotos to let you in on the secret weapon of double-digit multiplying without a calculator.
So here goes:
25 x 12
draw four squares
allocate a number to each square
this is where the Ninja lines are drawn diagonally across the four squares
multiply the single numbers along the dotted lines
repeat for each square
once you've multiplied all the single digits with each the other
add little tails to the edges of the squares to elongate the Ninja lines
add up the numers along the diagonal divisions
et voilà: 300
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