- = 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
166
CChapter 17hapter 17
CCHECKING HECKING ANSWERS A NSWERS
(( DDIVISION)IVISION)
Casting out nines is one of the most useful tools available for working
with mathematics. I use it almost every day. Casting out nines is easy
to use for addition and multiplication. Now we are going to look at
how we use the method to check division calculations.
CHANGING TO MULTIPLICATION
When we looked at casting out nines to check a problem with
subtraction, we found we often had to reverse the problem to
addition. With division, we need to reverse the problem to one of
multiplication. How do we do that?
Let’s say we divide 24 by 6 to get an answer of 4. Th e reverse of that
would be to multiply the answer by the divisor to get the original
number we divided. Th at is, the reverse of 24 ÷ 6 = 4 is 4 × 6 = 24.
Th at is not diffi cult.
cc17.indd Sec1:166 17 .indd Sec 1 : 166 1/9/07 8:40:53 AM 1 / 9 / 07 8 : 40 : 53 AM
- = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( )
brent
(Brent)
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