How to Multiply Decimals

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You don't need a calculator to multiply decimals. Find out how to multiply decimals with help from a mathematics educator in this free video clip.

Part of the Video Series: Mathematics Equations & More
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Video Transcript

Hi, I'm Jimmy Chang and we're here to talk about how to multiply decimals. Now one thing to keep in mind with multiplying decimals is, it actually works a lot, like the same way as you would a standard long multiplication. So we're going to do an example and you'll see how basically it's very similar, there's just one little tweak that we've got to think about. Now, suppose I wanted to multiply 1.(point)23 times 4.(point)5. Now, you set it up like you would a regular multiplication problem. You have 1.(point)23 times, now this is where folks might want to do things a little bit different, but I encourage you to do the same way. They want to line up 4.(point)5 with, where the decimals line up, but I tell you here, you do not want to do that. You actually want to multiply 4.(point)5 just like this. And we're going to address the decimal places at the end of the problem, but right now, for all intents and purposes, you will treat it like you normally would a long multiplication problem. So, let's see what we have. 5 times 3, you have 15, carry the 1 over. 5 times 2 is 10, add the one, 11. So you write the 1 but you carry the 1 on top. 5 times 1 is 5, add the 1, gives you 6. Now, as you would with regular multiplication, when you multiply the 4, you want to move over one space. So, you have 4 times 3 is 12, you have another 1 here. 4 times 2 is 8, add the 1, is 9. And 4 times 1 is going to give you 4. Now, as you know with long multiplication, you would just add the rows that you have, so 5 plus 0 is 5, 1 plus 2 is 3, 6 plus 9 is 15, carry the 1, 1 plus 4 is 5. Now, here's where the final answer starts to come together and now you get to address the decimal places. For the first number you have two decimal places, for the second number you have one decimal place, so two decimal places, you want to add the total number of decimal places. So, 2 plus 1, you have 3 decimal places that you've gotta keep in mind. So, starting from here, you simply move the decimal place, one, two, like we discussed, three. So your actual, final answer is going to be 5.(point)535. So, basically, when it comes to multiplying decimals, you just have to keep in mind, where the decimal places are and address them at the very end, otherwise it works the same way as regular multiplication. So, I'm Jimmy Chang and that's a demonstration on multiplying decimals.


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