This is a short compound lesson, they can see addends for nines and tens, they can see all the combinations and why it works out that way and they can make sense of it for themselves.

We then went on to build pyramids like you see in this post and we only did nines and tens, this reinforces the lessons on making change and the algorithms surrounding "numbers are made up of other numbers" and "want to be a ten" plus gives them the first 10 multiplication facts for nines all in one short lesson.

Any teach can add this to their "canned lessons" and get good results. Here is the video:

By the time they see it the third time this will be super easy...imagine what they could know by 2nd grade if they had math like this an hour a day instead of an hour a week.

Of course at the end I pointed out a bit about square numbers with 81 and 9 because this was a lesson on nines. We talked about what the symbol means, that squares have sides that are the same, and that you can shape numbers into squares and that it's easy to count one side.

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Crewton Ramone's House Of Math.