小肥問我 th 是甚麼意思，我向他解釋 1, 2 及 3 之後要加上 1st (first), 2nd (second)及 3rd (third)，21, 22 及 23 ，31, 32 及33 打後都是用這編排。特別的地方是 11, 12 及 13 則是用 th, 跟其他數目字一樣，因為英文的讀法是 eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, 跟以後的叫法例如 twenty-one, twenty-two, twenty-three 等都不同。
突然想到為何 11 – 19在讀法及寫法在編排上是與其它的不同呢？在網路找到這解釋：
How Did the Numbers Eleven, Twelve, and Thirteen Get Their Names and Where Did They Come From?
The reason the nine numbers after ten are known as eleven, twelve, and the teens is clarified by looking at Roman numerals.
In other words, they are all plus or minus units of ten and were interpreted into archaic English with this in mind.
Eleven (XI) or “leave one” means ten is one less than eleven.
Twelve (XII) means ten is two less than twelve.
Thirteen is three plus ten (or “teen”), four plus ten is fourteen, and so on.