 Okay guys, so we're going to do our first dimensional analysis problem together so let me read it to you It says what is the mass and grams of a 325 milligram aspirin tablet? So I've taken the liberty of writing down the number that was given to us in the problem 325 milligrams okay, but it wants us to convert it to grams. Do you guys know the conversion factor between grams and milligrams? Do you guys know it? Yeah, okay, so what is that conversion factor? One gram equals Okay, so we're gonna have to use that in this problem So we want the mass not in milligrams, but in grams right so in order to Get that we're going to have to put that conversion factor in a form. That's like a ratio So remember the two ratios that we could make this so what's one of them? Can you guys help me out one gram one gram divided by? 1,000 milligrams or the other one would be what? 1000 makes One gram makes that's a milligram a shortened version So what do we have on top here? So if you think about this as a ratio this over one Right, what do we have on top unit wise? Milligrams, okay, do we want milligrams in our final answer? No, so what do we have to do to them? We got to cancel them out right so in order to cancel them out Do we put them up here or down here on the bottom? So which one of these two conversion factors are we going to use? This one on the left or on the right? Okay, so let's use this guy here And watch what we do we put 1,000 milligrams There one gram and what happens to milligrams? So 325 divided by a thousand if you can't do this in your head feel free to give you a calculator out Okay, so let's all do it together 325 divided by a thousand and point three two five So how many significant figures does my calculation have to have? So it's got to be three the one thing you got to remember is those conversion factors never play in to the number of significant figures that you have in your final answer, okay? So since this only the only number that was given to you and the problem has three Then your answer has to have three as well Okay, so when I look at my calculator, it says 0.325 Grams, so that's how many grams there are in that aspirin tablet That's 325 milliliters and then box your answer and then everybody's okay There any questions on doing this kind of dimensional analysis? So notice what we're doing. We're changing from one unit to another set of units Okay, so you can do this if you're given or if you know the conversion factor So metric to metric like this one is grams to milligrams. You got to know those conversion factors. Does everybody understand what I'm saying?