yī
1
Every number up to a hundred, with audio. Learn ten digits and one rule — the tens first, then the ones — and you can say them all.
100 is 一百 (yì bǎi). Before 百 the 一 takes the fourth tone.
25 is 二十五 (èr shí wǔ): "two tens five".
11 is 十一 (shí yī). At the start of a number the one before 十 is dropped.
Tomyo
Numbers stick when you use them. Tomyo reviews your words on a schedule so what you learn is still there a month later.