 This video is going to talk about adding and subtracting fractions. When we add and subtract fractions we have to remember that there's different ways to do it. Sometimes they have the same number on the bottom and sometimes they don't. The same ones are the nice and easy ones because what we do here is we really want to know how many 11ths do we have. So we just have to add the tops. So 6 plus 9 is going to be 15 and that means that we have 15 11ths. Subtracting is no different. We have the same denominator so we're going to make that an 8 and 7 minus 3 is going to be 4. Always remember to reduce your fractions. So 4 over 8 is 1 half. So we think about least common denominator and we have to then think about the smallest number that both denominators divide into. So we really want to think about multiples. The multiples of each of these numbers. So 8 would be 8, 8 times 2 would be 16, 8 times 3 would be 24, 8 times 4 would be 32, 8 times 5 would be 40. We'll see if we're far enough. Let's think about the multiples of 12. So 12, 2 times 12 is 24. Oh look, we just found something that they both have in common. So the least common denominator, the first one we came across that they had in common was 24. So I come over here and talk about adding and subtracting and we have different denominators. We need that least common denominator so we can make them have the same one. So I need to multiply by a factor of A over A. I'm trying to get this. We said our least common denominator here. Oh, this is a different fraction. This is a 12. Somehow got a typo in there. So we said our least common denominator between 8 and 12 was 24. So when I think of this I'm going to say 8 times it was 3 that gave me 24, but it has to be a factor of 1. So I have to multiply the top and the bottom. So if I rewrite that problem then I get 3 over 24. And then if I take 12 I needed that to be 2 times 12 is 24. But then I have to multiply the top by the 2 as well to make it a factor of 1. So I'm not changing the fraction, just changing the way it looks. And 14 times 2 is going to be 28 over 12. And now when I add them 3 plus, oh not 12, that was 24 because we multiplied. Sorry about that. That's a 24. In fact let me clean that up. Oops wrong color. And then when I add them together 28 and 3 is 31 over 24 and that cannot be reduced. So let's just try a couple more times. The denominator here is 1. So that means that the least common denominator between 11 and 1, well that's easy. 1 times anything is going to be anything so let's let it be 11. So I don't have to do anything to this fraction because it already has the right denominator. And I have to multiply this one by 11 over 11 so that my denominator comes out right. So that gives me 22 over 11. And if I add these two I'm going to have 28 over 11 as my final answer. And then finally over here 10 and 15 you could list them all out or you could think about this is 10, 20, 30. 15 goes into 30 so the least common denominator must be 30. So I need to multiply the first fraction by 3 on the bottom so the top has to be multiplied by 32. And that gives me 12 over 30. And then 15 times 2 would give me 30 so I have to multiply by 2 over 2. 2 times 2 is 4 over my 30. And now remember this time we're going to subtract so 12 minus 4 is going to give us 8 over 30. They're both even so we know that they're divisible by 2 so that's going to be 4 over 15. And now you know how to add and subtract.