You should be able to add tens and subtract before you watch these videos.
In the first video, I say we are going to stop at about 5:20 but we keep going. Sorry!
Also in both videos, I miss something in the number line. Between 81 and 99 is 90. I fixed that in the PDF. Sorry again!
Also, in the first video, I say “shush” to my brother who was trying to talk to me. Sorry!
Most kids can’t count by nines. This post shows a new way.