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  • - [Instructor] Flynn's sister loaned him some money,

  • and he paid her back over time.

  • Flynn graphed the relationship between how much time

  • had passed, in weeks, since the loan and how much money

  • he still owed his sister.

  • What feature of the graph represents

  • how long it took Flynn to pay back the loan?

  • Pause this video, see if you can figure that out.

  • All right, now let's go through each of these choices.

  • So the first one is the slope.

  • So the slope tells us

  • how much do we change in the vertical direction

  • for any given change in the horizontal direction.

  • So for example, if we start from here,

  • we can see that if one week goes by,

  • we go from one week to two weeks,

  • we can see that our loan went down.

  • It went from $15 to $10.

  • So when we had plus one weeks in time,

  • our loan went down by $5.

  • And then that happens over the next week.

  • And that rate of how quickly the loan is paid,

  • that's what the slope tells us.

  • And it would be constant over the course

  • of the entire time period is what makes this a line,

  • is that slope is always going to be constant.

  • So the slope is useful for the rate

  • at which the loan is being paid back,

  • but it's not the clearest way to figure out

  • how long it took Flynn to pay back the loan.

  • So I would rule that one out.

  • The x-intercept, that's where the graph intersects

  • the horizontal axis,

  • which is often referred to as the x-axis.

  • Or another way to think about it,

  • that tells us, that says, what is the x-value

  • when our vertical value, our y-value, is equal to zero?

  • And our y-value is the money owed.

  • So it says, hey how much time has passed when we owe,

  • when we don't owe any more money

  • or when Flynn doesn't owe any more money to his sister?

  • Well that's exactly what they're asking for.

  • How long did it take Flynn to pay back the loan?

  • And that's what that x-intercept tells us.

  • It took him four weeks.

  • After four weeks, he didn't owe any more money

  • to his sister.

  • So I like this choice, but let's just review

  • the other ones.

  • The y-intercept, well that's where the graph

  • intersects the y-axis right over there.

  • This tells us what's going on at time t equals zero.

  • At time t equal zero or time equal zero,

  • when the horizontal variable is equal to zero,

  • we see that Flynn owes $20.

  • So this one isn't valuable for figuring out when he,

  • how long it takes to pay it back.

  • This one is useful for figuring out

  • how much did he owe initially.

  • So we'll rule that one out.

  • And we already picked one choice,

  • so we can rule out none of the above.

- [Instructor] Flynn's sister loaned him some money,

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A2 flynn loan slope intercept owe sister

Slope and intercept in tables

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    林宜悉 posted on 2020/03/27
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