二 vs. 两 - Chinese Grammar Points (42)

1. In ordinal numbers, second is always 第二 and never 第两. 
2. Some nouns can form ordinal numbers without 第. 
3. 二 is generally used in Sequence and Counting Number. 
4. 二月 = February; 两个月 = two months; 
5. 两 = "Both";  
6. 两 can be used in front of 百-hundred/千-thousand/万-10 thousand/亿-100 million; 
7. 2 years old should use 两;
8. In a larger number (greater than 10) that involves two, then 二 is used.