Arithmetic operations 
A number expressed in base or radix N consists in digits ranging from 0 to N1. A valid octal (base8) number can be for example, 6174. Number expressed in any base can be added or subtracted by following the same (usually unknown rules) as done for decimals operations.
Sum of BaseN numbersThe sum is performed digit by digit starting from right to left until the last digit is added. The rules are:
Example: Add the hexadecimals 4FC + EB5. Recall the values of the letters: A=10, B=11, C=12, D=13, E=14, F=15.

Subtraction of BaseN numbers
For the sum, the subtraction follows the same rules as for decimals.
Suppose we want to subtract A8D2  3EAC (hexadecimal). We'll align our numbers: The 'h' means hexadecimal number A 8 D 2 h  3 E A C h  Now in the ones place, we can't subtract C (12) from 2 so we borrow 1 from the sixteens place. Since that has a place value (a "weight") of sixteen, we can exchange it for 16 ones. (This is kind of like changing a $16 bill into sixteen $1 bills.) This leaves us with 12 sixteens (D = 13 minus the 1 we borrowed) and gives us 18 ones (2 plus the 16 we got from the borrow). We now subtract 1812 = 6: (Note that I use decimal here. Some people 12 18 write these as Ch and 12h.) A 8 \ \ h (There was a D and a 2 under the '\'s)  3 E A C h  6 h In the sixteens place, we don't need to borrow because we can subtract 10 (A) from 12: 12 18 A 8 \ \ h  3 E A C h  2 6 h In the 256's place, we again need to borrow. We'll borrow 1 from the 4096's place and exchange it for sixteen 256's (one 4096 equals sixteen 256's). This leaves us 9 in the 4096's place (A = 10 minus the 1 that we borrowed), and gives us 24 in the 256's place (8 plus the 16 from the borrow). We then can subtract 2414 = 10 = A. So we have: 9 24 12 18 \ \ \ \ h  3 E A C h  A 2 6 h Finally, we subtract 93 = 6 in the 4096's place: 9 24 12 18 \ \ \ \ h  3 E A C h  6 A 2 6 h Why did we get 16 from each borrow? Because each time, the next place value was 16 times as large. This is because hexadecimal is base16. One final note: If the subtrahend (the bottom number) is larger than the minuend (the top number), flip the numbers around and make the final answer negative, just as you would in decimal. The subtraction for other bases follow the same rules, taking into consideration that the borrow adds up 8 for octals and 2 for binaries. 