September 27, 2012

You learn every day...

Sitting down with Expat girl to do her homework, she very proudly asked me to give her two double digit numbers which she would multiply with the help of a new method she had learnt at school earlier today. My curiosity was peaked ... we were still doing single digits yesterday?!?

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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