You've gotten such good instruction on your questions that I'm going to bring up something you didn't ask about. When you are knitting two of the same thing (i.e. and arm front) you can knit them at the same time by casting on twice with two balls of yarn or from both ends of one ball and then doing the same row twice. That way you won't have to start the same piece all over again you can see that they match.
Can you link to the pattern or a picture? I'd like to see what you're working on.
I should never overestimate my basic arithmetic skills.