207
+ - = 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
W WORKING THROUGH ORKING THROUGH
AA PROBLEM PROBLEM
What you say inside your head while you perform mental
mathematical calculations is very important. You can double the
time it takes to solve a problem by saying the wrong things,
and halve the time by saying the right things. That is why I tell
you what to say, for instance, when you are multiplying by 11
in your head. To multiply 24 by 11, you would automatically
see that 2 plus 4 is less than 10, so you would look at the 2 and
immediately start saying, “Two hundred and.. .” While you are
saying that, you would see that 2 plus 4 means that you should say,
“... sixty-.. .,” and in the same breath you would say, “... four.”
So you would just say, “Two hundred and sixty-four.”
To multiply 14 by 15, you would simply add 5 to 14 to get 19. You
say in your head, “One hundred and ninety.. .” Four times 5 is
- Adding 20 gives, “Two hundred and ten.” You would say “One-
ninety, two-ten.” Th e less you say, the faster you will be. Practice by
yourself.
AAppendix Bppendix B
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