Help With Adding Unlike Fractions

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When two fractions are "unlike," it is important to know that you can still add them together. Get help with adding unlike fractions with help from a mathematics educator in this free video clip.

Part of the Video Series: Mathematics Lessons
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Video Transcript

Hi, I'm Jimmy Chang and we're here to talk about getting help with adding unlike fractions. Now, with unlike fractions, the one fundamental concept you really want to keep in mind is you have to think about using the least common denominator because that is really the only way that you can add unlike fractions. So, we're going to do a couple of examples and you'll see how this works. Suppose, you want to add one third and one fourth. Now, they're obviously two unlike fractions and the one thing you don't want to add is add across right away because that'll definitely give you the wrong answer. What you want to think about is the least common denominator of the three and the four or the LCD for short. And you're going to think about what number, what's the lowest number that three and four will go into and that will be after some thought, twelve. Now, what you can do is think about both denominators being twelve right away and ask yourself, "Three times what number is going to give you twelve?" Now, as you know, three times four is going to give you twelve. However, as you know, not only you have to multiply that denominator by that number, you have to multiply by the numerator by that the same number. So, one third is really four twelfths and you have to ask yourself the same question about four. Four times what is twelve. I'm sure by now it's going to be three; but again, if you multiply by the bottom, you have to multiply the top by that exact same number. So, one fourth is really three twelfths. So now, you can add this fractions together; the only thing you keep in mind of course is keep your denominator the same, but your numerators which add across. So, one third plus one fourth is seven twelfths. Now, another quick example here, if you have one fourth plus one sixth; same kind of idea here. Think about what's the first number that four and six will go into. Now, after some thought you might think, "Well, the first number that comes to mind will really be twelve because both four and six go into twelve, twelve right away. So, just like before, think about both denominators being twelve and think about four times what number is going to give you twelve; that's three. So, one fourth is really three twelfths and then, six times what number is going to give you twelve, that's going to be two. Multiply both the top and bottom, you got to remember that, by two and one times two is going to give you two. So, one fourth plus one sixth is really like saying, three twelfths plus two twelfths which gives you five twelfths. So, these are a couple of quick demonstrations for you; I'm Jimmy Chang and that's getting help with adding unlike fractions.

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