I'm hoping for verification here that I'm not crazy on some very very basic chemistry questions. I've worked 7 problems on a practice test (the real thing is next Tuesday). Only 2 of my answers agree with the answer key. Here are the most dramatic examples. Please tell me I'm not crazy. 1. The problem statement, all variables and given/known data Four very basic problems: Problem 1: [(1.900 + 0.0200) / (23.75 + 0.25)] + 0.06223 = ??? a.) 1 b.) 2 c.) 3 d.) 4 e.) 5 Problem 2: 2.94 x 10-6 + 5.118 x 10-5 + 8.80 x 10-7 a.) 5.5 x 10^-5 b.) 5.50 x 10^-5 c.) 5.500 x 10^-5 d.) 5.5000 x 10^-5 e.) none of these Problem 3: How many picograms are in 275 ug (micrograms)? a.) 2.75 x 10^8 pg b.) 2.75 x 10^-4 pg c.) 2.75 x 10^5 pg d.) .275 pg e.) 2.75 x 10^8 pg Problem 4: Which of the following correctly pairs the physical quantity with the SI unit associated with it? I. Volume, L II. Mass, kg III. Temperature, *C a.) I b.) II c.) III d.) I and II e.) II and III 2. Relevant equations None 3. The attempt at a solution I've been forced to retake an intro level chemistry class for engineers (degree plan problems to graduate). I thought I was done with sig figs. I'm studying for the first major test and I'm 100% on everything except these three problems with sig figs and basic prefixes. Problem 1 attempt: Applying the rules one step at a time: Numerator: 1.900 + 0.0200 = 1.9200 truncated to 1.920 (by place) Denominator: 23.75 + 0.25 = 24.00 no truncation (by place) So reducing I'm left with: (1.920 / 24.00) + 0.06223 Performing the division: (1.920 / 24.00) = 0.0800000000 truncated to 0.08000 (4 places by number of digits for multiplication and division) Reducing down: 0.08000 + 0.06223 = 0.142230000 truncated to 0.14223 (by place) This suggests my final answer has 5 significant figures. The answer from the answer key is 3 sig figs. I can't purposely work this problem incorrectly and come up with 3 sig figs. Problem 2 attempt: Just writing them out longhand (instead of scientific) .00000294 .00005118 .000000880 __________ .000055000 truncated by place to .00005500, and converting to scientific notation (as the answers are listed) I have 5.500 x 10^-5. The correct answer is listed as 5.50 x 10^-5. Problem 3 attempt: micro is 10^-6. pico is 10^-12. So there are 6 places without messing with the decimal. Slide the decimal over 2 more places to arrive at 2.75 x 10^8. The correct answer is listed as 2.75 x 10^7. I'm a little weaker on sig figs since I haven't used them since taking gen chem 5 years ago, but I'm virtually certain this answer is wrong. I've been using these prefixes for junior and senior level classes for 2-3 years in electrical engineering. Problem 3 makes me call the whole answer key into question. Problem 4 attempt: I and II. Answer key says only I. Volume is liters. Mass is kilogram. Temperature is kelvin. Does chemistry treat mass as grams instead of kilograms? Is this some special exception or was this test written in a hurry? I'm tearing my hair out over these.