Find X if 2X = X2.

In other words, can you find a number such that if you append '2' to the end of that number, it would be the same as doubling that number?

Question proposed by a friend on a high-speed rail trip in China.

Restart Civilization

Suppose every human on Earth suddenly disappears except you and the other people at your high school/university/workplace. What is the first thing you and your friends do? In the long-term, how would this event affect race/religion/politics?

Inspired by the Dr. Stone anime.

Big Number

Using any expressions, symbols, functions you'd like (except infinity/limits), handwrite the largest number you can in one minute.

Inspired by Quora.