Write a product of two numbers in non decimal base If $A=(b-1) (b-1) (b-1)$ and $B=(b-1) (b-1)$ are written in base $b$, what is $A\times B$ in base $b$? 
I've tried developing $A \times  B$ in decimal base but couldn't get this product back in base $b$.
Beside this, is there a general procedure to compute product in non decimal base.
Thanks in advance for your help,

Your two numbers as the largest possible three digit and largest possible two digit number written in base $b$. I.e. they are $1000_b-1_b$ and $100_b-1_b$. Algebraically these are equal to $b^3-1$ and $b^2-1$ respectively. As such their product will be given by:
$$(b^3-1)(b^2-1)=b^5-b^3-b^2+1$$
This however has negatives in it so its hard to read it as a base $b$ number. Lets manipulate until it is all positive values multiplied by powers of $b$.
$$=(b-1+1)b^4-b^3-b^2+1$$
$$=(b-1)b^4+b^4-b^3-b^2+1$$
$$=(b-1)b^4+(b-2+2)b^3-b^3-b^2+1$$
$$=(b-1)b^4+(b-2)b^3+2b^3-b^3-b^2+1$$
$$=(b-1)b^4+(b-2)b^3+b^3-b^2+1$$
$$=(b-1)b^3+(b-2)b^3+(b-1+1)b^2-b^2+1$$
$$=(b-1)b^3+(b-2)b^3+(b-1)b^2+b^2-b^2+1$$
$$=(b-1)b^3+(b-2)b^3+(b-1)b^2+1$$
This is now a sum of positive numbers times a power of $b$ so we can read off the coefficients to give up the digits in base $b$. So the digits in your product are $b-1$, $b-2$, $b-1$, $0$, $1$. E.g. in base 10 it would be 98901, in base 4 it would be 32301, etc.
