Since general division & multiplication take so many cycles (often with a wide variation between cases) 2600 programmers try to avoid them if at all possible. Where one of the operands is a constant a dedicated routine can often be created (such as the div/mod 15 routine sometimes used for sprite positioning) or a table used. But even then, it is a good idea to try and figure out a way to do without.
Just continuing my day late (or 4-5 months) / dollar short comments:
re: multiplication and division: remember, both are really just high powered forms of addition and subtraction, respectively. So to multiply a number X by Y, sometimes it's going to be easier and quicker to just add X to itself Y times. (unless of course you're multiplying/dividing by two, but that's a whole 'nother story)
Also, regarding that diagram (and I love the pitfall placed on it, it really makes it come to life); one interesting bit of math estimation is that, in the vertical blank (where a lot of programs place all their calculations) you have
37 scanline * 76 machine cycles = 2812 cycles
Now, most instructions take between 2-4 cycles. Be conservative, call it 3.5. That's time for about 800 instructions...another 650 if you start doing work in the overscan part. That's room for a fair amount of logic, actually (on my current project, I keep getting paranoid about "what if I run out of time in the VBLANK?") The tricky part (as this tutorial goes on to talk about) is trying to get stuff done during the visible scanline kernal, cause while a single 3 cycle instruction takes place, 9 pixels zoom past. Zip!