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Finding slope and intercepts from tables

Given a linear relationship in a table, practice finding the slope and intercepts.

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  • winston baby style avatar for user Roshni Jacob
    I didn't understand the Linear equations word problems:tables. What he explains in the video doesn't seem to apply there at all.
    (54 votes)
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  • blobby green style avatar for user Liana Sargsyan
    these problems are so easy but the actual problems are hard and make no sense
    (17 votes)
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  • mr pants orange style avatar for user jean paul jauriga
    I didn’t understand the problem with linear equations word table..... I need help with that
    (17 votes)
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    • starky ultimate style avatar for user Zéca
      OK, lets see if I can help you out. The problem in this video involves calculating slope. So, in this case, let´s say the tire rotation is the x value, and the distance to the tree is the y value. Slope is y over x , which means, rise over run. So, lets pick up an interval and calculate the slope. from 4 to 8 tire rotations, the x variation was, evidently, 4 units, and the y variation was -10 units.Lets apply y/x, which gives us -2.5 . That means the slope is -2.5 on all the line that the table represents.
      Once the slope is known, it is easy to calculate the answers to the questions, because for every rotation of the tire, you know how many units it travels. I will not publish the answers to all the questions in the problems, because it would spoill the fun of solving them.

      Hope this helps, and do not hesitate to ask more questions if you still do not get it.
      (11 votes)
  • blobby green style avatar for user rasmusbergdahl
    Khanacademy.org
    As previous mentions, the video(s) does not cover the practice for 'Linear equations word problems: tables'.
    The formula in the 'Hint' is provided but no video-explanation of it, which makes it tricky to understand.
    Please assist.
    (16 votes)
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  • sneak peak purple style avatar for user raziyah.macy
    I never know if I can add a decimal and if I should round
    (5 votes)
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  • blobby blue style avatar for user rachel
    Why couldn't we just use the slope-intercept form instead of the point-slope formula? What does a point-slope formula even mean/do?
    (5 votes)
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    • hopper cool style avatar for user Stanley Z.
      Point-slope is just another way to write linear functions. Point-slope form is y-y1=m(x-x1) where you find the slope of the line, and you can pick any point (x1,y1) that lies on the line and plug it into the formula, and that’s all you do for point-slope. Hope that answers your question.
      (4 votes)
  • blobby green style avatar for user LL Blue Coral
    how large is her tire? is it possible to find that as well?
    (3 votes)
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    • starky ultimate style avatar for user Taders09
      LL Blue Coral: here you go.
      If the tire rolls 2.5 meters in one rotation, that means the circumference of the tire is 2.5 meters. The circumference of a circle is diameter * π, so the diameter is 2.5m/π, which means the tire is about 0.80 meters, or 80 centimeters. (Quite a big bike!)
      Also I know that @Reid Greenwood posted this in the comments, I just posted it here so more people could see it.
      Also Thanks, that was super interesting.
      (7 votes)
  • blobby green style avatar for user Dan Dro
    Hi I have a question regarding one of the practice problems. I dont think the whole problem is needed here.

    First you have this thing :

    y-y1=m(x-x1)

    Than it transforms into :

    a) Temperature-2.5=7.5(Time-1)

    Than it just says "when we solve for time we get.."

    b) Time=Temperature+5/7.5

    Can someone explain please how do you get time alone ? how do you exactly move things around to get from a) to b) ?

    I spent a lot of time on this one but still dont get it. Thank you.
    (6 votes)
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  • blobby green style avatar for user camilobritocarrascal
    Can we solve the problem with rule of three?
    (3 votes)
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  • piceratops ultimate style avatar for user Ixn
    Is there a faster way to find the intercepts other than the method shown above?
    (4 votes)
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Video transcript

- [Instructor] We're told Kaya rode her bicycle toward a tree at a constant speed. The table below shows the relationship between her distance to the tree and how many times her front tire rotated. So once her tire rotated four times, she was 22 1/2 meters from the tree. Then once she's rotated eight times, she's 12 1/2 meters from the tree. When it rotated 12 times, then she's only 2 1/2 meters to the tree. So she's getting closer and closer the more rotations that her tire has had. So then they ask us some questions here. So they ask us how far away was the tree to begin with? How far does Kaya travel with each rotation? How many rotations did it take to get to the tree? So like always, pause this video, and see if you can answer these questions on your own before we do it together. So let's start with the first question. How far away was the tree to begin with? So the way that I would think about it is, after four rotations, we're 22 1/2 meters from the tree. We see that if we increase by another four rotations, so let's say plus four rotations, we see that we have gotten 10 meters closer to the tree, or our distance to the tree has gone down by 10 meters. So I'll write negative 10 meters here. If we want to figure out how far the tree was to begin with, we have to go back to zero rotations. So if we're going back by four, so we're subtracting four from the rotations. And if we're going at a constant rate, well, then we would add 10 meters. So we would add 10 meters. If we add four rotations, we get 10 meters closer. If we take away four rotations, to get us back to zero rotations, then we will go 10 meters further. So that would be at 32.5 meters. So 32.5 meters is how far the tree was to begin with when Kaya had zero rotations. The next question is how far does Kaya travel with each rotation? All right, well, we already saw that with four rotations, she's traveling 10 meters, so we could say 10 meters in four rotations. So if we divide both of these by four, what would we get? Well, that's the same thing as 2 1/2 meters in one rotation. So this is 2.5 meters. And last but not least, how many rotations did it take to get to the tree? Well, we know that after 12 rotations, she's only 2 1/2 meters away from the tree. We also know that in every one rotation, she gets 2 1/2 meters closer. So she only needs one more rotation to cover this next 2 1/2 meters. So, if we go plus one rotations, we're going to go down 2 1/2 meters. We're going to go 2 1/2 meters closer to the tree, and we will be at the tree. So how many rotations did it take to get to the tree in total? 13 rotations. Now one thing that's interesting is to think about what we just did in a graphical context that you might have seen before. And if we were to put on the horizontal axis rotations and if we were to put on the vertical axis distance to the tree, distance to tree, I'll just call the vertical axis the y-axis and the horizontal axis the x-axis, well, we could see here that we have zero, four, eight, 12, I could go to 16. And then we saw that at zero rotations, we are 32.5 meters from the tree, so 32.5. This is all going to be in meters. So this first question was really another way of asking what is our y-intercept? And this next question, how far does Kaya travel with each rotation, well, we saw that when you increase your rotations by four, your distance to the tree goes down by 10 meters. So when this is plus four, we went down, we went down 10 meters. So it's negative 10 meters. So really what we were thinking about right here, this is, you could think about the magnitude of the slope. The slope of this line, the slope of this line that would describe her distance to the tree as based on the number of rotations, the slope is going to be our change in our distance, which is negative 10, four, our change in rotations, over four. So the slope of this line is negative 2.5 meters per rotation. But when they say how far does Kaya travel with each rotation, she's getting 2 1/2 meters closer. Her distance from the tree goes down by 2 1/2 meters. And this last question, how many rotations did it take to get to the tree, well, at what point is our y value, our distance to the tree, zero? And we saw that it is at 13 rotations. So this is another way of thinking about what was the x-intercept? So the line, it's a line because we know that she's traveling at a constant rate, looks something like that. So they really were asking us the y-intercept, the slope, and the x-intercept.