How do number systems work?

Question

Number systems

I'm in a stupor and can't figure out how it works.
103 in octal is 12 in octal, the answer is 71, but I can't understand how it is, please explain.

Answer 1

Positional number system

103
-12
---
 71

We subtract two from three, the result is 1.
It is impossible to subtract one from zero, therefore we borrow from the highest order and subtract one from 10 ₈ (or 8 ₁₀ , octal system), the result is 7.
Since we borrowed from the category, we subtract one from one, we get zero .
If you cannot count immediately in octal, then convert everything to decimal, then back
103 ₈ - 12 ₈ \u003d 67 ₁₀ - 10 ₁₀ \u003d 57 ₁₀ \u003d 71 ₈