Boxi Math

Stage 1 · The World of Numbers / #3

The Hidden Diagonal in the Nines Table

S-3 · Units can be redefined S-5 · Patterns can be put into words S-6 · Mistakes are fine — try it
Coming soon

The video is in production. Follow along on GitHub to hear when it is out.

The idea

Nine is ten minus one: each extra row brings one more ten and takes away one more dot, so the tens go up by one and the ones go down by one.

A common mix-up

Times tables have no reason behind them; you just memorise them.

Where it stops working

Eight is ten minus two, so the ones drop by two each time and run out at eight times six; up one, down one belongs to nine alone.

School year
China 2–3 US 3 UK 3–4 Singapore 2–3