Numbers to 100 million and beyond
The desktop version has "Tips and notes“ which have useful information. Learning about the different tones of 一 is all very well, but so it's relevant to the theme of "numbers" course contributors please add something like this? 在此预先道谢！
100, 000, 000=一亿yi1(2)yi4
Also + 加 - 减 x 乘 % 除 = 等于
Hope everyone enjoys learning Chinese and in spite of the numerous areas where this course can improve, I'd like to thank the contributors for creating this course, so thank you all!
Edit: The tips and notes section has been updated. It has more (relevant) information which is always an improvement.
Here are some 数字成语，simply 成语 (what we'd probably call idioms) with numbers in them. The definitions are off the top of my head, so feel free to point out any corrections or improvements.
一心一意 (yi4 xin1 yi4 yi4) - To do something with all their/his/her heart and will, very determined, single-minded
三心两意 (san1 xin1 liang3 yi4) - To have three hearts and two minds about something, to be uncertain or fickle-minded
四面八方 (si4 mian4 ba1 fang1) - Refers to north, south, east west (四面), making up 八方 with northeast, northwest, southeast, southwest, meaning (from, in, to) all directions
五颜六色 (wu3 yan2 liu4 se4) - 颜色 means colour in modern Chinese, so it means (very) colourful
七七八八 (qi1 qi1 ba1 ba1 or qi4 qi4 ba4 ba4) - rather colloquial, meaning almost finished, e.g. for sale of goods
九牛一毛 (jiu3 niu2 yi4 mao2) - One hair from nine cows; something minute, very insignificant, or something small in the midst of many bigger things (a midget among giants?)
十全十美 (shi2 quan2 shi2 mei3) - Ten is symbolic of completion, attainment of the highest level, or "level ten of wholeness and beauty", hence referring to perfection
百花齐放 (bai3 hua1 qi2 fang4) - A hundred (numerous) flowers blooming simultaneously, describing the colourful scene of many flowers in full bloom. It was adopted into The Hundred Flowers Campaign, also termed the Hundred Flowers Movement by the Communist Party of China around 1956-7 through which it encouraged the citizens of the People's Republic of China to openly express their opinions of the communist regime
千载难逢 (qian1 zai3/4 nan2 feng2) - An opportunity that is very precious and difficult to get, such that it would be difficult to get it even in a thousand years
万众一心 (wan4 zhong4 yi4 xin1) - Ten thousand people of one heart, one mind; referring to a large group of people who are united
亿兆一心 (yi4 zhao4 yi4 xin1) - All citizens united with one heart and one mind
不计其数 (bu2 ji4 qi2 shu4) - Too many to number, innumerable, as the sand on the seashore
寥寥无几 (liao2 liao2 wu2 ji3) - Very few, implying so rare and so few as to be difficult to find out and count how many (little) there are
Source and for more examples: https://yuedu.mipang.com/hchj/chengyu/shuzi/
Thanks for pointing that out! I need to check for typos before posting, sorry.
As for yi4 vs yi1, I usually pronounce the former as well, but the "standard" one is yi1 (from what I learnt at school), hence I'd say yi4 is colloquial but the "accurate" one to learn is yi1.
In the word "一百", yi1 becomes yi4 because of a phenomenon called tone sandhi. However, since rules for tone sandhi vary a lot between different people and dialects, it's not required in any "standardized" version of reading.
I never knew the name for it, thanks for sharing it.
However, if memory serves I was taught that yi4 is colloquial and yi1 is actually the current "standard". It is confusing because the older standard when my parents were learning in school was yi4 and now (or then, when I learnt it) they changed "back" to yi1. Both are understood, at any rate.