 Okay, so this is another set, another video with another set of examples from the basic math techniques that are from your textbook, the basic laboratory message for biotech second edition by Seidman and Moore. And this video deals with the sample problems on percents. So the question at the top of page 234 says show two strategies to convert the fraction 3467 into a percent. And the first strategy is the kind of a proportional thing 3467 to 100 because we want to take this to 100 if we're doing percentages. So we're going to cross multiply, so we get 34 times 100 is equal to 67 times our unknown. So 34 times 100 over 67 is equal to our question mark. And then that's right. So let's call our calculator right back up here and solve that 34 times 100. 30, 3400 divided by 67. I'm getting both up there at the same time divided by 67 equals 50.7%. And that is strategy one. I'm just going to go to the side of it here and do strategy two. So we just take 34 divided by 67, which is going to equal to 0.507. And so we have to multiply by 100 equals 50.7%. So if you just divide the fraction, take the fractional form and do your division and multiply by 100, then you're going to get the percent. So this is two strategies to convert that fractional form into a percent. So here's their question. So the laboratory solution is composed of water and ethylene glycol. How could you prepare 500 mils of a 30% ethylene glycol solution? So strategy one, 30% is 30 100. So I'll keep saying this when you're doing the percent, take it to 100. So 30% is 30 of 100. So if you were 30 mils, if it were 100 mils, it's how much do you need if it's 500 mils? So we can cross multiply and say 30 times 500 mils is equal to 100. So we do this 30 times 500 over 100, in this case, mils. Then that's equal to 15,000 mils over 100 or 150 milliliters. With percent, the other strategy we can use is just multiply by the decimal form of 30%. So we have 30%, its decimal form is 0.30. So in this case, if we want 500 mils at 30%, then we multiply by 0.30, and we get 150 mils. So if we're making up 500 mils, we'll have 150 mils of ethylene glycol, and then we'll bring it to volume with 350 mils of water. I want to do a variant on that of making up a solution of a dry, of a powder, rather than ethylene glycol, which is a liquid that you're going to do the two mils. I'm going to look at making a 20% weight-to-volume solution, and let's say that we want to make up 500 mils of a 20% weight-to-volume. So we can do it the same way with strategy one. If we're going 20 per 100, it's supposed to be a 1, 20 to 100 is how much? The 500. So we do the same thing 20 times 500, if you divide it by the 100 is equal to a question mark. So we'd have 10,000 over 100 or 100 grams, right? Strategy two, same kind of thing, 500 mils times 0.2 is going to give us 100 grams. So we've got the same number of 100 grams. Now we're making a solution weight-to-volume, and we decided that we need 100 grams of our solute, and so we want 500 mils of solution. The thing is, we cannot add 100 grams to 500 mils because that 100 grams has some volume itself. So we're going to have to dissolve the 100 grams in a partial volume, right? And then we're going to have to then rank a volume of 500 mils because we want our final volume to be 500 mils. And so we have to dissolve that liquid in some volume less than 500 and then rank it with the volume, okay? Let's carry on, all right, with one of their other sample problems, which is the one on page 233, about percent, and the human genome. Okay, so here's that question, and let's see if I can get it about where I want it here. And there are actually three questions in this. So the first question, okay, it gives us some information and it asks us the first question. So there are about three times 10 to the ninth DNA base pairs, the BP is in abbreviation for base pairs, in the human genome. Human chromosome 21 contains about 2% of the human genome about how many base pairs comprise chromosome 21. So here's our two methodologies. 2% to 100 is equal to how many base pairs, right, out of 3 times 10 to the ninth base pairs. All right, so 2 times 3 times 10 to the ninth is equal to 100 times the question mark, or 2 times 3 times 10 to the ninth divided by 100 is equal to our question mark, right? And so that is equal to 6 times 10 to the ninth divided by 100, which is equal to 6 times 10 to the seventh. Or using the decimal form of the percentage, we can say, right, 3 times 10 to the ninth base pairs, right, times 2% in the decimal form, 0.02 is equal to 6 times 10 to the seventh base pairs. So two ways on working percentages, you can always do the proportion taking it to 100, or if you're comfortable with using the decimal form, you can do that as well. Okay, so part B, the goal of the human genome project was to find the base pair sequence of the entire human genome. If chromosome 21 is sequenced, and if the techniques are correct 99.9% of the time, how many base pair determined will be incorrect? So first you look at if it's correct 100% of the time, right? We need to subtract 99.9% to determine what percent were incorrect. So that's 0.1% incorrect. So if the 0.1% are incorrect, right, and the genome is 6 times, or the base pairs in chromosome 21, we determined to be 6 times 10 to the seventh base pairs, right? Then the incorrect are going to be times the decimal form of 1%, which is 0.01, right? So that will give us 6 times 10 to the fourth incorrect. So here's part 3. Approximately one out of every 700 babies born has an extra copy of chromosome 21. Such children have Down syndrome, which is associated with mental retardation and heart disease. About what percent of all children are born with Down syndrome? So it's saying 1 in 700 have it, so it wants to know is equal to what percent? So once again, two methods, right? We can say 1 in 700 is how many questions? How many of 100, right? And so we can say 1 times 100 is equal to 700 times question. Remember cost multiplying, right? So we divide both sides, right, 1 by 700 is equal to question mark. So 100 divided by 700 is equal to 0.142, 0.142%. Or when you say 1 out of 700, divide that to give us 00142, right? And move the decimal two places to change that to the percentage form. So we get 0.142%. So there again, those are some sample forms. They're done, they're in the text. They have even worked through it. I just put these videos together to kind of talk about, put a voice behind those problems. Talk about the strategies involved in these. And so, you know, look at these, get comfortable with them, work the samples, work the samples, the answers are in the back of the book. To check your work, the more of these you work, the more comfortable you'll become. Thanks for listening.