 Okay, so this says calculate the atomic weight of naturally current chlorine if 75.77 percent of chlorine atoms are chlorine 35 and 24.23 percent of chlorine atoms are chlorine 37. Okay? So the way I want you to do these problems, so I would write it down the same way I'm writing it down here. Let's write down what the problem actually gives us. So it says chlorine 35 and chlorine 37 and it gives us the percent of abundance of chlorine 35 as being 75.77 percent and it gives us chlorine 37 as being 24.23 percent. Okay, so the way you do this is to, oh and then we know the mass of these. Alright, it's going to be this one's 35.00 AMU. Is everybody okay with that? So, the way you do this, so the atomic mass average is going to be the abundance, abundance times the mass plus the abundance times the mass. So this is the abundance of one isotope times the mass of that same isotope plus the abundance of the other isotope times the mass of the other isotope. Is everybody okay with that? So notice, this is percent abundance and this is abundance. Okay, so you're going to have to make that ratio. Okay, so you can either make the ratio first or you can make it last. Okay, so the way I'm going to do it is last. So, so how do you get a ratio from a percentage? Divide it by 100. Exactly, that's how you do it. Okay, so this is the abundance, not the percent of abundance. So I'm going to do it, first I'm going to just fly it out and then divide by 100. And it's divided by 100% as a matter of fact. Right, because we've got to remove that percent sign. So when we do that, percent are going to cancel and let's figure it out. So, 75.77 times 35 plus 24.23 times 37 divided by 100. I got 35.48 as the average mass of corn given these abundances and masses. Okay, so everybody okay with doing something like this? And if you compare it up to the periodic table, you'll notice that it's a tiny bit different because there's different isotopes of chlorine that they do. Questions about doing something like this? Pretty cool, good. Sure, okay I want it.