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


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:



  1. Getting students to line up numbers by their place values.
  2. Having students be able to quickly write down anti-nines.
  3. 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).
  4. Using carries and crossing them out when used.
  5. If they can carry out the magic trick, that is outstanding and a bonus (not the primary objective of this lesson). 



Anti-Nines_Addition.pdf80.81 KB