I'd probably go with math, if you're including everyday math like adding, subtracting, multiplying, dividing. Higher level math probably isn't directly useful to most people in an obvious way although higher maths are used in science and engineering careers to bring us the technologies many of us take for granted.
Writing is important but you can have communication via other means. You can communicate orally and pass down information that way. You can also get the message across through non-verbal means.
Originally Posted by Gauche
We have SJs for that dirty work with math.
Even the higher level maths?
5w6 or 9w1 sp/so/sx, I think