Math Antics - Adding and Subtracting Fractions - By mathantics
Transcript
| 00:03 | Uh huh . In this video we're going to learn | |
| 00:07 | the basics about how to add fractions . Now . | |
| 00:10 | A lot of math books will teach you how to | |
| 00:12 | add fractions before they teach you how to multiply them | |
| 00:14 | . But here at math antics we think you should | |
| 00:16 | learn the other way around . You . Remember how | |
| 00:19 | easy it is to multiply fractions right ? You just | |
| 00:21 | multiply the top numbers together and you multiply the bottom | |
| 00:24 | numbers together and you have your answer . So you | |
| 00:27 | might be wondering , well can't we just do that | |
| 00:29 | with addition to ? Can't we just add the top | |
| 00:31 | numbers together and add the bottom numbers together and get | |
| 00:34 | our answer . Well all right , let's try it | |
| 00:37 | and see . But I got a bad feeling about | |
| 00:39 | this . Let's try adding one half to one half | |
| 00:43 | . So if we added the top numbers we'd get | |
| 00:45 | to and if we added the bottom numbers we'd get | |
| 00:47 | four . But well that can't be right because two | |
| 00:50 | older four simplifies to one half . And if you | |
| 00:53 | add 1/2 and one half you should get a whole | |
| 00:56 | not half . Oh we must have broke some sort | |
| 01:00 | of Matthew I'm out of here . Okay , here's | |
| 01:07 | what we did wrong . It turns out that there's | |
| 01:09 | some important math rules called order of operations that say | |
| 01:12 | you have to do multiplication and division before you do | |
| 01:16 | addition and subtraction . Now because fractions are just division | |
| 01:20 | problems . If you just added the top numbers and | |
| 01:23 | added the bottom numbers , you'd be breaking those rules | |
| 01:26 | because you would be doing the addition before the division | |
| 01:29 | . So what are we going to do instead ? | |
| 01:31 | Well , fortunately there's a trick that lets us work | |
| 01:34 | around the order of operation rules and add fractions without | |
| 01:37 | dividing . But there's a catch , it only works | |
| 01:40 | for fractions that have the same bottom numbers . The | |
| 01:44 | trick is if fractions have the same bottom numbers , | |
| 01:47 | we can add them by just adding the top numbers | |
| 01:49 | together and keeping the same bottom number in our answer | |
| 01:53 | for example , to add one half and one half | |
| 01:56 | , we just add the top numbers and one plus | |
| 01:58 | one gives us too . But we don't add the | |
| 02:01 | bottom numbers , we just use the same bottom number | |
| 02:03 | in the answer . Which is to so to over | |
| 02:06 | two is a whole fraction . And that makes sense | |
| 02:09 | because if you add one half and one half you | |
| 02:11 | get a whole Let's see a few more examples like | |
| 02:15 | this . one , 5/16 plus 2/16 . Again , | |
| 02:19 | since the bottom numbers are the same , it's easy | |
| 02:22 | to add these fractions . All we do is at | |
| 02:24 | the top numbers together , five plus two equals seven | |
| 02:27 | and that's the top number of our answer , then | |
| 02:29 | we just keep 16 as the bottom number of our | |
| 02:31 | answer . So 5/16 plus 2/16 equals 7/16 . Pretty | |
| 02:37 | easy . Huh ? But what about subtracting fractions ? | |
| 02:41 | Does that work the same way ? Yep . If | |
| 02:43 | the bottom numbers are the same , all you have | |
| 02:45 | to do is subtract the top numbers and keep the | |
| 02:47 | same bottom number . And your answer here is an | |
| 02:50 | example of subtracting fractions with the same bottom numbers . | |
| 02:53 | 5 : 9 -2 overnight . First we subtract the | |
| 02:57 | top number's 5 -2 equals three . Then we just | |
| 03:01 | write the same bottom number and our answer nine . | |
| 03:04 | So 5/9 minus 2/9 is 3/9 , yep , adding | |
| 03:09 | and subtracting fractions with the same bottom numbers is easy | |
| 03:12 | . And there's a special name for problems like this | |
| 03:15 | . It's called adding or subtracting like fractions . A | |
| 03:19 | teacher once told me that they're called like fractions because | |
| 03:22 | the bottom numbers are the same or alike . But | |
| 03:25 | I think it's because they secretly like each other just | |
| 03:28 | kidding But seriously like fractions are easy to add with | |
| 03:32 | the trick we just learned . But what happens if | |
| 03:34 | you want to add to unlike fractions ? What do | |
| 03:36 | you do if you have fractions with different bottom numbers | |
| 03:39 | ? Unfortunately the only way we can add unlike fractions | |
| 03:42 | without doing the division first is to change them so | |
| 03:45 | that they do have the same bottom numbers . In | |
| 03:47 | other words , we need to change our unlike fractions | |
| 03:50 | into like fractions so we can just use our trick | |
| 03:53 | in math language . That's called finding a common denominator | |
| 03:57 | . And remember that a denominator is just a fancy | |
| 03:59 | math word for the bottom number of a fraction and | |
| 04:02 | common just means that they're the same . So how | |
| 04:06 | do we find a common denominator so that we can | |
| 04:08 | add or subtract unlike fractions , that's what we're going | |
| 04:11 | to learn in the next video . But before you | |
| 04:14 | move on , be sure to do the exercises for | |
| 04:16 | this section . Learn more at math antics dot com | |
| 00:0-1 | . |
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