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### Paula says

Kevin.....Probably because some genius mathematician, Long ago....thought the X seemed more appropriate than the question mark..????? Obviously, I am not related to that genius........LOL!

### MickS says

Because it is, that's way of the world, they same question could have been asked of any use of the other letters if they were used for the same purpose.

### John Connor says

I believe the answer is found in the ancient Greek/Roman culture primarily because of their number system; however, I have always loved this solution to this math problem.

The question states: Find X

Here is the equation: 10 = 3X - 2

The answer is X=4; however, the answer I prefer is:

The problem solver simply circles the letter X and declares "Here it is"

Yes, rather like 2+2. The answer =4. No it isn't, is, it =2+2, but has an element of fourness about it.

### portables says

Is it because X marks the spot? so when you've found it then you know where the treasure is?

### luchorin says

well the premise of the question is false, the other letters are used as placeholders too. in number theory the convention is to use k, l, m, n, p, q for integers. supposedly the tradition of using x started with rene descartes. but algebra predates him, so obviously they were using other symbols before that.