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Comparing linear functions word problem: walk

Sal is given a table of values that represents four people walking to school, and is asked to determine which one started out farther from the school. Created by Sal Khan.

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  • leafers ultimate style avatar for user Ivan
    How would you express a rate as an equation?
    (4 votes)
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  • blobby green style avatar for user keelanp13
    Which function has a greater rate of change? Which function has a greater y-intercept?
    (5 votes)
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  • male robot hal style avatar for user Sun
    At , Sal said Gordon did start out farther from school than Elizabeth. But Gordon only started out 4 miles away and Elizabeth started out 5 miles away. So wouldn't Gordon didn't started out farther from school than Elizabeth?
    (3 votes)
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    • piceratops ultimate style avatar for user rayfish.law
      Gordon is actually going to the school. You can see that he gets closer to school as each hour passes. There is a constant rate of change if you graph the hours that passed and Gordon's distance from school. The rate of change is -2. As each hour passes, he gets 2 miles closer to school. This means that after 0 hours, Gordon is actually 6 miles away from school, and Elizabeth is 5 miles away from school. Gordon did actually start out farther from school than Elizabeth.
      (2 votes)
  • male robot hal style avatar for user Sun
    At if Hannah every time is exactly 5 miles away from school how can we know that she is napping? She is actually moving. She's probably is just walking back and forth like maybe she walk 1 mile further/closer to school then she walk back to his original distance.
    (3 votes)
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  • blobby green style avatar for user Roy McCoy
    Hannah could be walking in a circle around the school, right?
    (2 votes)
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    • stelly blue style avatar for user Kim Seidel
      1) The problem tells you that Hannah is walking away from the school. If she was walking in a circle, she would still be the same distance away from the school as when she started. To walk away from the school, the distance needs to be increasing.

      2) You are learning about linear word problems. Linear means the equation creates a line, not a circle, or a curve.
      (0 votes)
  • blobby green style avatar for user mohamed abdelmoneim
    we can solve it by y-intercept (b). from y=mx+b
    (1 vote)
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  • leaf red style avatar for user Dylanツ
    is there a more systematic way to solve this?ツ
    (1 vote)
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  • blobby green style avatar for user aidan davis
    how come it says the y intercept is bigger when number 1 is 3 and number 2 is 3 and i still get it wrong
    (1 vote)
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  • marcimus purple style avatar for user Evan Evan
    Gordon: Poor guy has to spend 3 hours walking to school!
    (0 votes)
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  • piceratops ultimate style avatar for user alexdragon0701
    Is there a more systematic way of solving this? :)
    (0 votes)
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Video transcript

Elizabeth starts out 5 miles away from school and walks away from school at 3 miles per hour. So she's already 5 miles away. And she's going to walk even further away at 3 miles per hour. The table below shows how far some other students are from school at various times. Each person is moving at a constant speed starting at time is equal to 0. Which students started out farther from school than Elizabeth? Select all that apply. So essentially, we need to figure out where these students were at time equals 0. So we know where they were at time 1, 2, and 3. And so let's think about their rate towards or away from school. And remember, this is distance from school. As we increase-- as we go from hour 1 to hour 2, Gordon gets 2 miles closer. So his distance to school is decreasing. So where was he at time equals 0? I'll put time equals 0 up here because I don't have any-- actually, I'll put it right here. I'll try to squeeze it into the chart. So where was he at time equals 0? Well, he would have been 2 miles further. So he would have been 6 miles away. Notice that it's consistent. In the first hour, he would have gotten 2 miles closer to school. Then the next hour, he would have gotten 2 miles even closer. And then the third hour, he actually gets 2 miles closer. And he actually gets to school. So Gordon started out 6 miles away at t equals 0. So Gordon did start out farther from school than Elizabeth. So we can circle Gordon. He meets the conditions. Now let's think about Giovanni. So at time 1, he's 5 miles away from school. Then at 1 hour, he's 5 miles away. After 2 hours, he's 6 miles away. So he's getting further from school. So this is a plus 1. And then after another hour, he is 7 miles away. So every hour that goes by, he's a mile further. He's going 1 mile an hour away from school. So where was he at time equal 0? Well, he would have been a mile closer to school relative to time equal 1. So he would have been 4 miles away. So he did not start out farther than Elizabeth, who started out 5 miles away. Now let's look at Hannah. Hannah, at every time, is just exactly 5 miles away from school. So she's napping or something. She is not actually moving. She started out napping at exactly the same distance as Elizabeth, but she did not start out farther from school than Elizabeth. So Hannah does not meet the criteria. Now let's look at Alberto. At time equals 1, he is 9 miles from school. And then after 1 hour, he gets a mile and 1/2 further from school. After another hour, he gets a mile and 1/2 even further. So where was he at time equals 0? Well, he would have been a mile and 1/2 closer to school. So 9 minus 1.5 is-- he would have been 7 and 1/2 miles away. So even though he is going away from-- well, he definitely started further from school than Elizabeth. Elizabeth started out 5 miles away. Alberto started off 7 and 1/2 miles away and is going even further and further and further. So the two students that start out farther from school than Elizabeth are Gordon and Alberto.