A friend recently shared "Prof D" math tips and shortcuts... there are actually quite a few...!
- https://www.youtube.com/@ProfD
- https://www.facebook.com/MathProfD

Especially check out the short videos or "shorts."
For example: Multiply by 9s... in seconds - https://www.youtube.com/shorts/0BftcPnIoQE

Looks like pure FUN for those gifted in math, while also providing a new way for those who struggle with math to see the patterns in the relationships between numbers.