What Is a Proportion?

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A proportion is a part considered in relation to its whole, or it can be defined as a statement of equality between two or more ratios. Discover how proportions are used in math with help from a math teacher in this free video on proportions in math.

Part of the Video Series: Fractions & Proportions
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What is a proportion? Hi, I'm Jimmy Chang, I've been teaching college math for 9 years and we're here to answer exactly that question. Now a proportion actually has a couple of meanings and we're just going to go over them very quickly with you today. But just to let you know that both definitions can be used in a mathematical sense. Now first definition of a proportion is it's a part considered in relation to it's whole. In other words, you can think about if you have a part of something, whether it be a room, you can compare the room compared to the entire house. Or you can have one glass compared to the entire set of glasses. So one definition could be how a part is compared to the entire whole for which it's a part of. Now the other definition is more technical mathematics definition is it's a statement of equality between two or more ratios. Now what that talks about is if you have two or more fractions compared to with each other, if the two fractions side by side are equal, then it's considered a proportion. So for example, an order for A over B equal to C over D for them to in proportion with each other, then the cross multiplication have to be the same. So for example, for these two fractions to be equal, if you perform the cross multiplication, the number that you get with D times A which is AD equal to B times C which is BC. What this basically tells you as it relates to the definition is for two fractions to be equal, the cross multiplication has to be equal. But that is a second more technical definition of proportion but whether it be the first one or the second one, they're both valid as definitions for a proportion. So my name is Jimmy Chang and that's how you define a proportion.

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