ffirs.indd

21

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  • = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( )
    % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9
    ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8
    9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7
    8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6
    7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5
    6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3
    What if you want to multiply numbers above the reference number;
    above 10 or 100? Does the method still work? Let’s fi nd out.
    MULTIPLYING NUMBERS IN THE TEENS
    Here is how we multiply numbers in the teens. We will use 13 × 15
    as an example and use 10 as our reference number.
    10 13 × 15 =
    Both 13 and 15 are above the reference number, 10, so we draw the
    circles above the numbers, instead of below as we have been doing.
    How much above 10 are they? Th ree and 5, so we write 3 and 5 in
    the circles above 13 and 15. Th irteen is 10 plus 3, so we write a plus
    sign in front of the 3; 15 is 10 plus 5, so we write a plus sign in front
    of the 5.
    NNUMBERS ABOVE THE UMBERS ABOVE THE
    RREFERENCE NUMBEREFERENCE NUMBER
    CChapter 3hapter 3