Difference between 二 and 两.

The simplest rule I know is:

Use 两(liǎng) when the number is followed by a noun. Otherwise, use 二 (èr).

Examples:

• 二）二加二得四。
• 两）地铁晚两分钟。

Disclaimer:

I am not qualified Mandarin Chinese Teacher or native Chinese speaker. It means my notes about Mandarin Chinese may contain mistakes. If you spot any error, let me know in comments below.