How to Solve Proportions Using Cross Products

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One effective method for solving proportions is through the use of something called "cross products." Solve proportions using cross products with help from a longtime mathematics educator in this free video clip.

Part of the Video Series: Number Theory Education
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Video Transcript

Hi, I'm Jimmy Chang, and we're here to talk about how to solve proportions using cross products. Now, in order to have proportions, that means you're going to have fractions involve and cross products often involves using cross multiplication. So, the idea here is oftentimes you're going to have two fractions on opposite ends of equal sides and to solve it, you want to use cross multiplication. So, here's an illustration. If you have for example, 5/12 = x/7, let's just say; the idea here is you have proportions, 5 and 12 and x/7 and using cross products involve cross multiplication. So, just as a reminder, what you want to think about in cross multiplication is, the denominator of one side is going to multiply with the numerator of the other side and it goes with the other way around as well. So, at this point, you have 12 times x, which is going to be equal to 12x and 7 times 5 is going to give you 35. So, at this point, cross multiplication allows you to, for the most part, get rid of the fractions and then solve. So, to solve for x, you want to divide both sides by 12; so, you have 35/12 is equal to x because the 12 is cancelled. Now, obviously folks prefer the x used written on the left side and so you can say that x is equal to 35/12. So, when it comes to solving proportions involving cross products, you set the fractions up and then use cross multiplication to solve it. So, I'm Jimmy Chang, and that's a brief tutorial on how to solve proportions using cross products.


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