I really am having a rather difficult time trying to understand how to add and subtract, multiply and divide significant figures. I know how to round them, how to identify how many significant figures there are in a given measurement, but not add/substract/multiply/divide them. I was using the following online quiz, (I have my score on it, which is pretty bad, I know but I'm trying to understand WHY I made the errors I did.) to practice for my quiz tomorrow. http://www.syvum.com/cgi/online/serve.cgi/members/gillilandd/quizzes/sigfigs.tdf If my score does not show, here are the problems I had trouble with: 1.2 cm + 3.78 cm + 45.38 cm my answer: 50. this is incorrect, so the computer says. 34.8 cm x 98 cm my answer: 3400 this too is incorrect. Can anyone please give me an explanation as to what my errors were? thanks.