Hi Chris,
I use graphs a lot but I was not even tempted for this one.
We all develop our own methods for doing things. :)
My answer for this one is really quite comical
http://web2.0calc.com/questions/mg-to-grams
This method that I developed independently is excellent for difficult rates questions - they just fall out.
But this is not such a difficult question and my method is rediculously involved.
I am sure asinus's method is better and I strongly suspect that the last answering guest just shock his head at the rigmarole I went through.
His/her answer is probably excellent although I have not really looked at it I will admit.
We all have our quirks :))