How To Add And Subtract Related Fractions

Hi, I'm Brooke, and in this video we're going to be looking at addition and subtraction of related fractions. So in this example, I'm trying to add 3/4 and 1,8. But I've got a problem. The denominators are not the same. So I need to find an equivalent fraction. And to do that I need to look at both of the denominators and find a common multiple. Now, a Common multiple of 4 and 8 is 8. So what I'm going to do is using my bar model, I'm going to divide my quarters into eighths. So now we can see that 1, 2, 3, 4, 5, 6, 8 is equivalent to 3 quarters. So now I can do 6/8, add 1, 8, and because the denominator is the same, I can add them easily. 7, 8. Now let's have a look at a subtraction problem in this question. I'm doing 5, 9 and I'm taking away 1/3. So here I've represented it again on my bar model and we can see that the denominators are not the same. So I need to find a common multiple of 3 and 9. A common multiple of 3 and 9 is 9. So I'm going to divide my third into nine equal parts. And here we found an equivalent fraction. One third is also equal to 1, 2, 3, 9. Now that the denominators are the same, I can subtract them. Five, nine, take away three ninths equals two ninths, and that's how you add and subtract related fractions.