 Okay, so let's do this first problem that's on the quiz. 56 grams sample of iron reacts with 24 grams of oxygen to form how many grams of iron oxide. So you don't really need to know anything about reaction equations or anything except for the conservation of mass at this point in time. So what it's saying, all we need to really think is A plus B goes to C, right? So it's saying a sample of iron, we can call that A, reacts with oxygen to go to iron oxide, okay? So it gives us the mass of iron at 56 grams and the mass of oxygen at 24 grams and it's wondering what is the mass here, okay? Remember conservation of mass, right? We've got to make sure this side of the equation adds up to the same mass as this side of the equation, okay? So in order to do that, what do we do? A little add sign, addition sign there. And most people got that right, okay? This is the part, this is the reason this question is on the quiz or whatever is because, yeah, we look at this and we say 80 grams, everybody knows that, right? But we're in chemistry class so we have to remember our significant figures, okay? So we look at this particular answer, this is only telling us that one of those figures is significant, the other one is insignificant, right? So in order to tell that all of them are significant, we've got to put our decimal place there, okay? We could have put this in scientific notation if we wanted to as well, 8.0 times 10 to the 1 or 10 to the just 10 frames, okay? Any questions on that one? So the little clincher was the significant figure.