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Writing two-variable inequalities word problem

Sal solves a word problem about scores in a chess tournament by creating a two-variable linear inequality.

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  • winston default style avatar for user B_Dubb_B
    I knew that there would eventually be a chess question, but I didn't think it would mention Fabi. Magnus Carlsen, Levon Aronian, and Hikaru Nakamura better be used too. : )
    (7 votes)
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  • piceratops seed style avatar for user geoDenisF
    I don't understand why we swap a sign when dividing both side by negative value? I know this is a rule but how I can derive it?
    (0 votes)
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    • mr pink green style avatar for user David Severin
      By trial and error: If -x≥5, 0 does not work (0≥5), 5 does not work (-5≥5), but -5 does work (-(-5)≥5), -4 does not work (-(-4))≥5 or 4≥4), -6 and more will all work, so x≤-5.
      Second way, if -x≥5, I can add x to both sides to get 0≥x+5, subtract 5 to get -5≥x. Flipping this around gives -x≤-5.
      (7 votes)
  • blobby green style avatar for user JULIANA
    this dont make no sense my ahh acting like i understand whats going on
    (0 votes)
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  • leaf blue style avatar for user Smit
    So, if he gets 1/2 point for a draw, why is it written 0.5d? Would one draw give him the half point he needs?

    Why isn't the inequality written W+D≥6.5?
    (0 votes)
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  • piceratops tree style avatar for user Maiuri, Dominic
    This didn't help me with my problem.
    Stacy's mom is baking treats for Stacy's birthday party. She has 9 eggs to use for this purpose. A batch of cookies requires 1 egg and a batch of brownies requires 2 eggs.
    Write an inequality and shade the area to represent the solution.


    Im stumped!
    (0 votes)
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    • mr pink green style avatar for user David Severin
      Let cookies be on the y axis and brownies be on the x. The maximum number of cookie batches is 9, so graph (0,9), the theoretical maximum for brownies is 4.5, so plot (4.5,0) - I say theoretically because the most brownie batches will be 4. Connect these two points, and put dots on any pair of whole numbers below this line. While shading can be done, it is hard to assume that you could make partial batches rather than whole batches and I would also assume you are going to use as many eggs as possible.
      (1 vote)
  • blobby green style avatar for user mattandzann
    How do I help my daughter with this: Suppose s and t are two numbers and that s>t. Determine whether each inequality must be true.
    A. s + 15 > t + 15
    (0 votes)
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  • blobby green style avatar for user cadetrajeev1810
    Is there any solution for -b <( x-y)b<b?
    Or
    How to solve it?
    (0 votes)
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Video transcript

- [Voiceover] Fabiano wants to score at least 6.5 points in a major chess tournament. He scores one point for each game that he wins, and he scores 0.5 points for each game that ends in a draw. Write an inequality that represents the number of games Fabiano should win and draw, D, to achieve his goal. So I encourage you to pause the video and see if you can do that. Write an inequality in terms of the number of games won, so capital "W", and the number of draws, capital "D", that represents what he needs to do to actually achieve his goal. All right, let's work through it together. So how many points he is going to get from winning? So if he wins "W", he's gonna win W games, and he gets one point for each of them, so it's gonna be one point per game, times the number of games. So one W I could just write as W. So this is the points from winning. From wins, I could say. And what are his points gonna be from the draws? Well, from the draws, he's gonna have D draws, and he gets 0.5 points for each of them. zero point five times D, this is going to be the points from the draws. Now, this right over here is going to be his total points, points from wins, points from draws. I'm assuming he gets no points for losses. And we want this number, the total number of points, his score, to be at least 6.5. So we want this to be greater than or equal to 6.5. If it says Fabiano wants to score more than 6.5, then it would have been greater than. But it says Fabiano wants to score at least 6.5, so that's greater than or equal to 6.5. He's ok if he scores 6.5. And there you have it, we have our inequality in terms of the number of games he needs to win and draw and this inequality needs to be true in order for him to score at least six and a half points in this major chess tournament.