How To Add And Subtract Unrelated Fractions

Hi, I'm Brooke, and in this video we're going to be looking at addition and subtraction of unrelated fractions. So in this example, I've got one third and one quarter and I'm trying to add them together, but the denominators are different. Here I've drawn a bar model to represent both fractions. So to add the two, I need to make them have the same denominator. And to do that I need to find a common multiple of both three and four. So a common multiple of both of them is 12. I'm going to divide each of my bar models into 12. Now we can see that I've got four twelfths and three twelfths, and now that the denominators are the same, I can add them together. 412 add 3 twelfths equals 7 twelfths. So to summarize, we needed to find the lowest common multiple of both of the denominators, add the numerators together and leave the denominator the same, which gave us an answer of seven twelfths. And that's how you add and subtract unrelated fractions.