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Writing proportional equations from tables

Writing an equation to describe the relationship between the number of scoops in an ice cream cone and the price. Created by Sal Khan.

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  • male robot hal style avatar for user ShadowFax
    since change x/ change y=slope, then if the line doesn't intersect zero then what r u supposed to do?
    (6 votes)
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  • primosaur sapling style avatar for user Arden Little Eagle
    Does the bigger number always goes on top or can it go on the bottom?
    (5 votes)
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  • duskpin ultimate style avatar for user Shadow mist
    So when I went to the practice: writing proportional equations, it said "A unicorn daycare center requires there to be 2 supervisors for every 18 unicorns. Write an equation that shows the relationship between the number of supervisors (n) and the number of unicorns (u). I put n=9u because n= 1 supervisor and 9u= 9 unicorns. It said i was wrong so i looked through the hints to see where i messed up and it says the answer is u=9n which means it takes 9 supervisors to care for 1 unicorn. My question is whether I misunderstood the work, or if the answer itself is wrong.
    (7 votes)
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  • hopper happy style avatar for user Eric Thurmond
    This is not as hard as you make it
    (5 votes)
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  • blobby green style avatar for user jordan.t.williams
    Can anyone explain how this guy just converts 1 and 3/4 into 7/4. I was following along well until he just starts converting expressions instead of actually explaining how it relates to the problem rather just saying 1 and 3/4 is equal to 7/4.
    (2 votes)
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  • leaf yellow style avatar for user Camille
    How do you know when the answer to the problem is in fraction form
    (2 votes)
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  • old spice man green style avatar for user axelcarmona-granillo
    what is 14/9 and and x=2
    (3 votes)
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  • leafers tree style avatar for user rebypox
    At he says that Y=7/4x
    That's wrong! X=7/4 Y. Why did he switch them around?
    In the equation shows clearly that when X=1 Y=7/4 You can't just switch the letters like that when they represent different things!
    (2 votes)
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    • duskpin ultimate style avatar for user Arnav Khera
      No, Sal didn't switch them around. He simply transposed x to the other side which resulted in the equation Y = 7/4 X. By the way, even if Sal made a mistake, you could have said it in subtler tone in the clarifications page of the video :)
      (2 votes)
  • duskpin ultimate style avatar for user #cat
    How do we write a more complex equation?
    (2 votes)
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  • purple pi teal style avatar for user Grace
    Can you do proportional equations with negative numbers? Why or why not?
    (2 votes)
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    • spunky sam red style avatar for user 🏮🔥Phoenix Warrior🔥🏮
      Yes, you can.This is possible because uhhhh I really am not sure how to explain this so I try to clarify using a example. Let say you start with 500$(M) on monday then you spend 50$ every day.That would be a proportional relationship of which the equation would be M x -10% or M x -1/10.That is the best I can explain it since I am only in 7th grade.So I hope this helps.
      (2 votes)

Video transcript

I scream, you scream, we all scream for ice cream. The following table describes the relationship between the number of scoops in an ice cream cone, represented by x. So this is the number of scoops in an ice cream cone. So that's x, and the price of the cone, represented by y. I'll do y in purple. Write the equation that describes this relationship. So let's see. When x is 0, y is 0. When x is 1, y is 1 and 3/4. So let me write this as an improper fraction, just so I can visualize it better. So this is 4/4 plus 3/4, which is equal to 7/4. When x is 2, y is 3 and 1/2. So let me see if I can write this in a little bit of a clearer way. So 2 times 3 is 6, plus 1 is 7, so this is 7/2-- which is the same thing as 14 over 4. And then here we have, when x is 3, y is equal to-- so 5 and 1/4-- if I would write it as an improper fraction-- 4 times 5 is 20, plus 1 is 21. So this is equal to 21 over 4. And then finally, if we were to write this as something over 4, this is equal to 28 over 4. 7 is the same thing as 28 over 4. So you see that this is a proportional relationship. The ratio between y and x. So let me write this. The ratio between y and x is always equal to 7/4. Notice here, y is 7/4 of x. 7/4-- it's a bigger number. Or you could say 1 and 3/4 of x. So let me make that clear. So y over x is equal to 7/4. Or, we can say that y is always 7/4 of x. We can multiply both sides by x, if we like. So if we multiply both sides by x, we get y is equal to 7/4 times x. And you see it here. When x is 4, 7/4 times 4 is 7. When x is 0, y is 0. When x is 3, 7/4 times 3 is 21 over 4, which is the same thing as 5 and 1/4. So there we go. And let me input it, just to make sure we can input it right. So y is equal to 7/4 x. We would just write y is equal to 7/4 times x. And let's check our answer. And we got it right.