Math Antics - Multiplying Fractions - By
Transcript
| 00:05 | you've probably noticed that we've been talking an awful lot | |
| 00:09 | about fractions around here lately . Well now I'm gonna | |
| 00:11 | tell you something you can do with fractions . That's | |
| 00:14 | really easy . No , no , not juggling fractions | |
| 00:22 | , although that is pretty easy for me . I'm | |
| 00:26 | talking about something even easier than that . I'm talking | |
| 00:29 | about multiplying fractions . Multiplying fractions is super easy . | |
| 00:34 | In fact , it's easier than adding fractions and that's | |
| 00:36 | why we're going to learn it first . The reason | |
| 00:39 | it's easier is because fractions are really just division problems | |
| 00:42 | and multiplication and division get along much better than addition | |
| 00:46 | and division . Now , since fractions are division , | |
| 00:49 | that means if I have the problem 1/4 times two | |
| 00:52 | thirds . It's the same as the problem one divided | |
| 00:55 | by four times two , divided by three . That | |
| 00:58 | means I have both multiplication and division in the same | |
| 01:01 | problem . And because they get along so well , | |
| 01:04 | that means I can just rearrange our problem to look | |
| 01:06 | like this . Now , it looks like to multiplication | |
| 01:10 | problems that are being divided and it looks just like | |
| 01:13 | a fraction . In fact , if we go ahead | |
| 01:16 | and do the multiplication one times two equals two and | |
| 01:20 | four times three equals 12 , then we do have | |
| 01:22 | a fraction and it's the answer to our problem . | |
| 01:25 | So what does all this mean ? Well , it | |
| 01:27 | means that to multiply fractions , all you have to | |
| 01:30 | do is multiply the top numbers and then multiply the | |
| 01:33 | bottom numbers . And today there's your answer as always | |
| 01:37 | , let's see an example or two . Let's try | |
| 01:40 | this problem . Two thirds times 4/5 . Now we | |
| 01:44 | could rewrite the problem like we just saw but that's | |
| 01:46 | not necessary . As long as we remember the procedure | |
| 01:49 | first , we know our answer is going to be | |
| 01:52 | a fraction . So let's go ahead and write a | |
| 01:53 | new fraction line for it . Next we multiply the | |
| 01:57 | top number's two times four equals eight . So it's | |
| 02:00 | the top number of our answer . And last we | |
| 02:03 | multiply the bottom numbers three times five equals 15 . | |
| 02:06 | So 15 is the bottom number of our answer . | |
| 02:09 | There we have it to over three times 4/5 equals | |
| 02:13 | 8/15 . See how easy that was and fun to | |
| 02:18 | even funner than video games . Okay , time for | |
| 02:22 | another example , Let's try 6/11 times 7/8 . From | |
| 02:28 | our multiplication table , we know that six times seven | |
| 02:30 | equals 42 . So 42 is the top number of | |
| 02:34 | our answer . And on the bottom we have 11 | |
| 02:36 | times eight , which is 88 . So 6/11 times | |
| 02:40 | 7/8 equals 42/88 . Oh , now some of you | |
| 02:46 | might see that this answer could be simplified , but | |
| 02:48 | we'll save simplifying fractions for another video . All right | |
| 02:52 | , let's see . One last example here it is | |
| 02:55 | one half times 4/3 times 3/5 . Wait a minute | |
| 03:00 | . This has three fractions multiply together and the middle | |
| 03:03 | one looks like an improper fraction because it's top numbers | |
| 03:06 | bigger than its bottom number . Does our procedure work | |
| 03:09 | for this problem to , yep , all we have | |
| 03:12 | to do is multiply all the top numbers together and | |
| 03:14 | then multiply all the bottom numbers together and we'll have | |
| 03:17 | our answer and this will work no matter how many | |
| 03:20 | fractions we have to multiply . So on the top | |
| 03:23 | we have one times four is four and four times | |
| 03:26 | three is 12 . And on the bottom two times | |
| 03:29 | three is 6 and six times 5 is 30 . | |
| 03:32 | That means our answer is 12/30 . So there you | |
| 03:36 | have it multiplying fractions is easy because fractions are just | |
| 03:40 | another way of writing vision problems . But remember there's | |
| 03:43 | another way to think about fractions . We can also | |
| 03:46 | use fractions to represent parts of things like half a | |
| 03:49 | pizza for instance . But does it make sense to | |
| 03:52 | multiply half a pizza by another half ? Actually it | |
| 03:56 | does . If you're thinking of fractions as parts of | |
| 03:59 | something , then multiplying fractions is really like taking part | |
| 04:03 | of another part , for example , here's half a | |
| 04:07 | pizza . You can see that if I take one | |
| 04:09 | half of that half , Then I get 1/4 of | |
| 04:12 | a pizza . And if we do the multiplication one | |
| 04:15 | half times one half , you see that we do | |
| 04:18 | get 1/4 . So that's why you can think of | |
| 04:21 | multiplying fractions as taking part of another part . In | |
| 04:25 | fact , sometimes especially in word or story problems . | |
| 04:28 | You'll see multiplying fractions written using the word of instead | |
| 04:32 | of times , they may ask what's 3/4 of two | |
| 04:36 | thirds ? And now , you know , they just | |
| 04:38 | mean what's 3/4 times two thirds . So whether you | |
| 04:43 | think of fractions as parts of something or as division | |
| 04:46 | problems , the procedure for doing the multiplication is exactly | |
| 04:49 | the same . Let's do a quick review of what | |
| 04:52 | we've learned . Multiplying fractions is even easier than adding | |
| 04:56 | fractions . It's easy because order of operations says that | |
| 05:01 | we can do the multiplication before the division . The | |
| 05:05 | procedure for multiplying fractions is to multiply the top numbers | |
| 05:08 | to get the answers , top number and multiply the | |
| 05:11 | bottom numbers to get the answers . Bottom number . | |
| 05:13 | If you think of fractions as parts of something , | |
| 05:16 | then multiplying a fraction by another fraction is the same | |
| 05:20 | as taking apart of apart . And sometimes especially in | |
| 05:24 | word problems , you might see the word of instead | |
| 05:27 | of the word times , even though multiplying fractions is | |
| 05:31 | so easy , it's a good idea to practice so | |
| 05:33 | be sure to do the exercises and I'll see you | |
| 05:36 | next time learn more at math antics dot com |
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