87
- = 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
Th e general rule for using a reference number for multiplication is
that you choose a reference number that is close to both numbers
being multiplied. If possible, you try to keep both numbers either
above or below the reference number so you end up with an
addition.
What do you do if the numbers aren’t close together? What do you
do if it is impossible to choose a reference number that is anywhere
close to both numbers?
Here is an example of how our method works using two reference
numbers:
8 × 37 =
First, we choose two reference numbers. Th e fi rst reference number
should be an easy number to use as a multiplier, such as 10 or 100.
In this case we choose 10 as our reference number for 8.
Th e second reference number should be a multiple of the fi rst
reference number. Th at is, it should be double the fi rst reference
CChapter 10hapter 10
MMULTIPLICATION ULTIPLICATION
UUSING TWO SING TWO
R REFERENCE NUMBERSEFERENCE NUMBERS
- = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( )