[Tomato_Tom]

Hi! I found this forum through Reddit and I was hoping to get some clarification on the use of significant figures.

So a bit of background, we had a short quiz a few weeks ago concerning handling numbers. There were two items that concerned mixed operations, and I handled it the way I thought it should have been done based on the resources I've seen online. Which was to apply the rules of addition & subtraction, and multiplication & division, step-by-step based on the order of operations (GEMDAS).

However my answer was marked incorrect in the test, due to it having to be rounded to 2 SF, rather than 3 SF. I brought it up with my teacher, and my understanding behind her reasoning is that we can only be as precise as our least precise measurement. Meaning that we round off the final answer to the lowest SF regardless, due to the measuring tools limiting our measurements in practice. I also brought it up with a senior in the same course about the same time, and her explanation was that I was looking at it too much from a mathematical perspective, and not a chemistry laboratory perspective. But what confuses me is that I assume the rules for significant figures should be consistent regardless of context? I'll attach the problem in question, and how I went about it. I would really appreciate some clarification on this matter, because its been bugging me all night. Thank you in advance!

https://imgur.com/a/pYYcY6J

[Borek]

I would say she is wrong and blindly applies wrong rules to addition/subtraction.

Don't worry too much about SF though, they are good to give you a basic intuition of the accuracy of the numbers you deal with, but are mostly useless when it comes to real accuracy in a real analytical work where it matters.

[Tomato_Tom]

Thanks for the clarification! It's good to know I didn't have the rules mixed up. I'll just follow my teacher's method though when I take similar tests, since it seems like I can't change her opinion on that matter.