风马牛不相及
Have nothing to do with each other.

【发音】fēng mǎ niú bù xiāng jí

【释义】这个词语原指齐楚两地相离甚远，马牛不会走失到对方地界。比喻两个事物毫不相干。
            In ancient times, there is such a long distance between Qi and Chu that horses and cattle wouldn’t enter the other side.

【例1】这和我们的谈话内容，有点风马牛不相及啊！
           I don't see it has anything to do with what we're talking about.

【例2】在音乐课上，一个数学的问题是风马牛不相及的。
           A question about arithmetic is irrelevant in a music lesson.