yego.me
💡 Stop wasting time. Read Youtube instead of watch. Download Chrome Extension

Writing y = mx proportional equations worked example 1 | Grade 8 (TX) | Khan Academy


2m read
·Nov 10, 2024

We are told in a rowing exercise Claudia completes 450 strokes in 15 minutes. Write an equation that can be used to find the number of strokes y she can row in x minutes. So, pause this video and see if you can figure that out.

All right, now let's think about this together. So what I'm actually going to do is a little bit of a table here, and I'm going to put the number or I'll put time here in minutes, and this is going to be our x variable. And then over here, I'm going to put strokes, and this is going to be our y variable.

So they've already told us one that after 15 minutes—and everything here is in minutes—that Claudia was able to do 450 strokes. Is there maybe another point we can think about? Well, let's think about what happens at zero minutes. How many strokes would Claudia have done? Well, she wouldn't have done any at that point. She hadn't had a chance to do any strokes.

And so now there's something interesting going on here. We can see that when time is increasing by 15, how much are the strokes increasing by? Well, they're increasing by 450. Or another way to think about it is what is our change in y over change in x, or a change in strokes per change in time? Well, we can calculate that now. That's going to be 450 strokes for every 15 minutes.

And this we can see: 450 divided by 15 is going to be 30. And we can even write the units down—this is in strokes per minute.

Now, you might also recognize that this is the same definition as what we normally consider to be slope. So how can I write this as an equation? Well, my y, the number of strokes, is just going to be this unit rate—how many strokes per minute—which is also going to be my slope. It's just going to be that which we could consider m times x.

And you could try it out for these two points: when x is zero, y is zero; when x is 15 minutes, y is 450 strokes. And we are done.

More Articles

View All
Just Let Go | The Philosophy of Fight Club
Life is short. It’s ending one minute at a time. Why waste it on fulfilling other people’s expectations? This is just one of those questions presented in a novel written by Chuck Palahniuk named Fight Club. The film version of Fight Club, directed by Dav…
Warren Buffett: How to Invest Tiny Sums of Money
I think if you’re working with a small amount of money, I think you can make very significant sums. But as soon as you start getting the money up into the millions, many millions, the curve on expectable results falls off just dramatically. So, I just cam…
How The Economic Machine Works by Ray Dalio
How the economic machine works, in 30 minutes. The economy works like a simple machine. But many people don’t understand it — or they don’t agree on how it works — and this has led to a lot of needless economic suffering. I feel a deep sense of responsibi…
50 Years Ago, This Was a Wasteland. He Changed Everything | Short Film Showcase
[Music] 50 years ago, you couldn’t hardly walk through this place. It was wall to wall. [Music] Brush! There wasn’t any grass, there wasn’t any water. Nobody wanted. [Applause] It on the truck, on the truck! He’s the finest dog in the United States of Am…
Example reflecting quadrilateral over x axis
We’re asked to plot the image of quadrilateral ABCD. So that’s this blue quadrilateral here under a reflection across the x-axis. So that’s the x-axis, and we have our little tool here on Khan Academy where we can construct a quadrilateral, and we need to…
Why I Stopped Spending Money
What’s up guys? It’s Graham here. So, I think it’s no surprise that for anyone to see my channel for a while, I’m pretty frugal. To be honest, even calling it that could be generous. I’m, uh, extremely thrifty, or maybe we could just call it fiscally cons…