Originally Posted by

**Dana_Scully** I've always been confused by how to determine the number of significant figures when the expressions involve both two types of operations and exponential notation. I've been through several introductory physics/chemistry courses and still don't know how to do this. I've asked the professors and heard other people ask the exact same question but only received a reply which sounded like they didn't know what I was asking. Anyway, it's really getting on my nerves, so could someone please work out for me exactly what you would do to solve questions like the following two? I think that will be much easier than me trying to explain the questions I have.

1. 320.55 - (6104.5/2.3)

2. [(285.3 * 10^5) - (1.200 * 10^3)] * 2.8954

For example, for the first question I first divide 6104.5 by 2.3, getting 2654.13043, which is rounded to 2.6 * 10^3 because it can only have two significant figures. But how do you calculate decimal places (to figure out how many significant figures the difference should have) when you are expressing one of the addends in exponential notation? Even if that issue is resolved, i am not sure how to express the answer. I hope I've explained myself clearly and am not making a stupid mistake.