Setting Up a Proportional Equation

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You need to set up a proportional equation in a very particular way in order to be as accurate as possible. Find out about setting up a proportional equation 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 setting up a proportional equation. Now, in terms of setting an equation up, it really depends on how the equation is worded and the words or phrases will give you an idea as to how to put the numbers in their proper places. So, again, it really depends on what it happens to be; but, let's give an example as to how one might work. So, you might have something that might be worded like this, 5 is 20 percent of what number? Now, you know the number 5 is going to be used, so you have the number 5. Now, is is generally a nice way of saying equal sign. Now, 20 percent, you can think of 20 percent as 20 over a 100 because as you know, any percent is that number over a 100. Now, this is obviously not the entire equation because then you have to figure out of what number. Now, in that particular case, that's when you have to think about its 5 over what number, let's just call it x, or you can use a letter n for number if you want; but, what you have here is a proportional equation because you have two proportions on either side in fraction form. And then to solve it, you may have been familiar with this already, but you use cross multiplication to be able to solve proportional equations. So, the idea goes something like this; the denominator multiplied with this numerator and this denominator multiplied with this numerator. So, x times 20 is going to give you 20x and then 100 times 5 is going to be 500. And then, you want to divide both sides by 20 to solve for x. So, you have x is equal to 500/20 and here what you want to think about is reduce when necessary. So, the zeros cancel and then 50/2 is going to give you 25. So, x is 25. So, 5 is 20 percent of what number? That number is going to be 25. But, the bottom line here is in order, in order to solve and setup proportional equations, you have to look at the words and figure out what numbers go where. The percent all, is their own fraction and the other parts make up the other fraction. So, I'm Jimmy Chang, and that's an example as to how to setup a proportional equation.


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