Point
Counting in Japanese is systematic. There are some exceptions but overall quite logical. Once you learn the units, you need to know when the unit changes as numbers increase.
For example, in English, "hundred" goes up to 900. And "thousand" goes up to 900,000 before it changes to "million".
In Japanese, "hyaku・ひゃく・百 (hundred)" goes up to 900. And "せん・千・sen (thousand)" only goes up to 9,000 and changes to "man・まん・万 (ten thousand)".
So, to call 10,000 in Japanese, you say "iti man (one 10,000)" instead of "jyū sen (ten 1,000)".
It will be easier to understand and master once you watch the video and study the accompanying table.
See you next time!
Please note