Indifference curves and marginal rate of substitution발음듣기
Indifference curves and marginal rate of substitution
Indifference curve. What it is, is it describes all of the points, all of the combinations of things to which I am indifferent.발음듣기
Now we're going to talk about all of the combinations that essentially give us the same total utility.발음듣기
Let's draw a graph that tells us all of the different combinations of 2 goods, to which we are indifferent.발음듣기
Like we've mentioned before, we're focusing on 2 goods, because if we did 3 goods we would have to do it in 3 dimensions and 4 goods would get very abstract.발음듣기
In the horizontal axis, this is going to be the quantity of fruit, and this is going to be in pounds of fruit.발음듣기
Let's say that right now, at some point, I am consuming 5 pounds of fruit per month and 15 bars of chocolate per month.발음듣기
I wouldn't care whether I have 15 bars of chocolate and 5 pounds of fruit, or whether I have 10 bars of chocolate and 7 pounds of fruit.발음듣기
I've introspected on what I like and what I derive benefit and satisfaction out of and I get the same total utility out of either of these points.발음듣기
In general I could plot all of the different combinations that give me the exact same total utility, and it might look something like this.발음듣기
Any point on this curve right over here, I'm indifferent, relative to my current predicament of 15 bars and 5 pounds of chocolate.발음듣기
Now let's think about it. Obviously, if I go all over here, 20 pounds of fruit and ... I don't know, that looks like about 2 bars of chocolate.발음듣기
If someone just swapped everything out, I would kind of just shrug my shoulders and say, "No big deal."발음듣기
That is clearly not preferable, because, for example, that point I just showed, I can show a point on the indifference curve where I am better off.발음듣기
For example, that point that I just did, that's 5 pounds of fruit and about 5 bars of chocolate.발음듣기
Assuming that the marginal benefit of more chocolate is positive, in the way I've drawn this, the assumption is that it is, then I'm obviously getting more benefit if I get even more chocolate per month.발음듣기
Not preferred. Using the same exact logic, anything out here, well that would be good, because we're neutral between all of these points on the curve.발음듣기
This green point right over here, I have the same number of bars as a point on the curve, but I have a lot more pounds of fruit.발음듣기
Assuming that I'm getting marginal benefit from those incremental pounds of fruit, we will make that assumption, then this right over here, anything out here is going to be preferred.발음듣기
Preferred. The whole area down here is obviously we've not preferred to anything on the curve.발음듣기
The last thing I want to think about in this video, is what the slope of this of this indifference curve tells us.발음듣기
If you give me a line like that, the slope is, how much does my vertical axis change for every change in my horizontal axis.발음듣기
At any point on this line, if I do the same ratio between the change in Y and the change in X, I'm going to get the same value.발음듣기
What we really do, to figure out the slope exactly to point, you can imagine it's really the slope of the tangent line at that point, a line that would just touch at that point.발음듣기
I'll do it in pink. Let's say I have a tangent line right from out starting predicament, just like that.발음듣기
Right there, the slope of the tangent line looks like that, or you can view that as the instantaneous slope right there.발음듣기
It looks like we're going to have to give up, based on the slope right over there, it looks like we're going to have to give up 5 bars.발음듣기
It's going to be your change in bars, your change in chocolate bars over your change in fruit.발음듣기
Over your change in fruit. In this situation, it is negative 5 bars for every 2 fruit that you get.발음듣기
Bars per fruit. It's essentially saying, exactly at that point, how are you willing to trade off bars for fruit.발음듣기
Say, exactly where you're sitting right now you would be indifferent only as you just slightly move, or for an extra drop of fruit an extra ounce of fruit, not even a whole pound, you would be willing to trade off 2.5 bars per fruit.발음듣기
What this says, so you're willing to give up, since it's negative you're giving up 2.5 bars of chocolate for every pound of fruit.발음듣기
Once you have a lot more fruit you're going to be much less willing to give up bars of chocolate.발음듣기
Over here you have a lot of bars and not a lot of fruit, so you're willing to give up a lot of bars for fruit.발음듣기
Once again, the slope is the change in the vertical axis, over the change in the horizontal axis.발음듣기
I'll say B for F. Over here you're willing to give up fewer bars for every incremental fruit.발음듣기
That makes sense. Over here you had a lot of chocolate bars, not a lot of fruit, so you were willing to give up more bars for your fruit.발음듣기
This number, how many bars you're willing to give up for an incremental fruit, at any point, at any point here, or you can view it as the slope of the indifference curve, the slope or the slope of a tangent line at that point of the indifference curve.발음듣기
Marginal rate of substitution. It's a very fancy word, but all it's really saying is, how much you're willing to give up of the vertical axis for an increment of the horizontal axis.발음듣기
Right at that point, for a super, super small amount, how many bars are you willing to give up?발음듣기
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