This is a brain teaser. In general, 1+ 1 is equal to 2, but the topic gives the proposition that 1+ 1 is not equal to 2. If we understand it according to the conventional thinking, we can't find out the reason, but it's because the calculation is wrong, 1+ 1 is not equal.

Extended data:

The origin of brain teasers:

Brainstorming originated in ancient India. Brainstorming is a series of complete comic jokes published by the culture of the times on 1989 12.06, which changed from the comic question on the previous page to the unexpected answer after flipping through it.

At that time, there was a social craze in Taiwan Province Province, and all the streets and alleys were asking each other brain teasers, which evolved into a pattern of cold jokes and was later introduced to Chinese mainland.

Baidu encyclopedia-brain teaser