another method to multiply

In the book "The Secret Life of Math",

(click here for my earlier blog post about this book)

a few ways of multiplying is introduced,

this is one we really like.

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Let's try something simply like 45 x 78

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Since both numbers are in tens,

so we need two boxes at each sides

which altogether makes four boxes.

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Write 45 across at the top and 78 down on the right

or vice versa.

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In each box, draw a slanted line from top right to bottom left
and continue drawing it out of the box.
Do the same with all the boxes.
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Now is time to do the calculation.
4 x 7 = 28,
write the answer in the box with the TEN (2) on top and UNIT (7) below.
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Repeat this step with all the numbers.
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Plus the numbers follow the SLANTED boxes,
in this case, the number is 0
.
5 + 4 + 2 = 11
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Leave the UNIT at its place,
move the TEN to the next line.
.
3 + 8 + 3 + 1 = 15
leave the 5 at its place and move the 1 to the next line.
.
2 + 1 = 3
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The answer is 3510

more sums