225
- = 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
E ESTIMATINGSTIMATING
Often, it makes far more sense to estimate than it does to give an
exact answer. Some answers can’t be given with absolute accuracy;
the value of pi is always approximate, as is the value of the square
root of 2. Both of these values are used and calculated regularly. Even
percentage discounts in your department store are rounded off to the
nearest cent or nearest 5 cents. When you are buying paint or other
materials from a hardware store, you have to estimate. It is a good idea
to estimate high to be sure you have enough nails, ribbon, or whatever
it is you are buying. An exact amount is sometimes not a good idea.
We used the idea of estimation when we looked at standard long
division. We rounded off the divisor to estimate each digit of the
answer, then we tested each estimate.
If I am buying computer screens for a school, how much will 58
computer screens cost me if they are $399 each? To get a rough
estimate, instead of multiplying 399 by 58, I would multiply 400
by 60. So, my estimate is 400 × 60, or 4 × 6 × 100 × 10, which
is 24,000. Because I rounded both amounts upward, I would say
AAppendix Ippendix I
bbapp09.indd 225app 09 .indd 225 1 1/5/07 11:37:47 AM/ 5 / 07 11 : 37 : 47 AM
- = x 0 1 2 3 4 5 6 7 8 9 ( ) % < > + - = x 0 1 2 3 4 5 6 7 8 9 ( )