# Anti-Nines and Addition Magic (10-6 through 10-8)

Posted on October 6th, 2009 by kramer

Anti-nines are pairing numbers that sum to 9 like:

0 and 9,1 and 8, 2 and 7, 3 and 6, 4 and 5, 5 and 4, 6 and 3, 7 and 2, 8 and 1, 9 and 0

Here is a magic trick with anti-nines that will dazzle anyone:

Tell them, "Please write down three random numbers each with the same number of digits. Put one under the other lined up with each place value column. Now, I will write down two more random numbers below yours. Then, I will add those five numbers in a matter of seconds. Now, you should add up these numbers to see if I am right."

(below, you will find out how this works)

The objectives for this exercise is not to have your child memorize this trick. The important objectives are:

- Getting students to line up numbers by their place values.
- Having students be able to quickly write down anti-nines.
- Having students practice adding numbers vertically by pairing friendly tens (almost each column of numbers here has some friendly 10s and a carry of 1 or 2).
- Using carries and crossing them out when used.
- If they can carry out the magic trick, that is outstanding and a bonus (not the primary objective of this lesson).

Attachment | Size |
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Anti-Nines_Addition.pdf | 80.81 KB |