Pairs that make 100

Bonjour! Et Bonne Annee! Happy New Year!

This week we have been working with our "Quel est la question?" routine at the start of most math classes.  One student is responsible for picking a 3-digit number between 100 and 999.  They write it on the board and the other students need to come up with at least one question that will give that number as an answer.  I'm asking students to consider using addition, subtraction, and multiplication in their questions.

For example number 184

10x10 + 80 + 4
200 - 16
100 + 20 + 20 + 20 + 20 + 4
184 x 1
etc

Also we are working on finding matching numbers that add up to 100.  In partners, one partner picks a number between 0 and 99.  The other partner must write the other number that makes the total add up to 100.  I'm asking the students to try doing this mentally, and then checking their answers afterwards using one of our RekenReks, the 100's chart, a number line, or whatever tool they would like to use.

For example:
36 + 64
71 + 29
18 + 82

The main idea is that the ONES need to add up to 10, while the TENS column add up to only 9, since the 10 ones will add one extra 'ten' for the sum.  Here is the 100-bead Rekenrek that can be used to check 36 + 64:

These pairs can be practiced at home, and extended to pairs that add up to 1,000 as well.