Chinese slang: 风马牛不相及
Have nothing to do with each other.
【发音】Pronunciation: fēng mǎ niú bù xiāng jí
Explanation: In ancient times, there is such a long distance between Qi and Chu that horses and cattle wouldn’t enter the other side. (Qi and Chu are two of the seven warring states during China's Warring State period or Zhanguo from 475 BC to 221 BC)
Example 1: I don't see it has anything to do with what we're talking about.
Example 2: A question about arithmetic is irrelevant in a music lesson.