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## AP®︎/College Microeconomics

### Unit 4: Lesson 2

Monopoly- Monopolies vs. perfect competition
- Economic profit for a monopoly
- Monopolist optimizing price: Total revenue
- Monopolist optimizing price: Marginal revenue
- Monopolist optimizing price: Dead weight loss
- Review of revenue and cost graphs for a monopoly
- Monopoly
- Efficiency and monopolies

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# Review of revenue and cost graphs for a monopoly

AP.MICRO:

PRD‑3 (EU)

, PRD‑3.B (LO)

, PRD‑3.B.6 (EK)

In this video, we review the key features, behavior, and consequences of a monopoly. Created by Sal Khan.

## Want to join the conversation?

- why does mc cross atc at its minimum?(2 votes)
- When marginal cost is below average total cost, the cost of an additional unit is lower than the average cost of all the units, so it causes average total cost to fall. If marginal cost is greater, the cost of an additional unit is higher, so average total cost will rise. So when they are equal, it will stay the same.

Think of it like your GPA. Say ATC=your GPA (the average of all your grades), and MC=the grade in your next course (one particular grade). If you have a B average and get a C in your next course, your GPA will fall (like when MC is lower than ATC). If you have a B average and get an A, your GPA will rise (like when MC is higher than ATC). If you get a B in your next course, there won't be any change because it's the same as the average (like when ATC=MC).(25 votes)

- Does Marginal revenue have something to do with the elasticity of the demand curve? I know that elasticity changes at different points of a straight line demand curve. What would happen to marginal revenue if the demand line is curved with unit elasticity (elasticity=1) at all points of the demand curve. would MR be a straight line?(5 votes)
- yes it would be a straight line

I suggest you watch the optional video on derivatives.

He keeps saying "if you consider your demand curve to be a straight line" and if i've understood the elasticity of demand, that would also mean when elasticity = 1

(I would also like a confirmation though, I've never had to juggle with elasticity and marginal revenue :/)(6 votes)

- What's the difference between the "Total Economic Profit" at9:45of this video and "Producer Surplus" introduced in the video of Dead weight loss of Monopoly? I'm so confused.(2 votes)
- This would be so much easier to explain with a graph . . . sigh.

Total Economic Profit is Total Revenue (quantity x price) minus Total Costs (ATC x quantity).

Producer Surplus, on the other hand, is the difference at all quantities between the reserve price (what the producer would be willing to sell the product for) and the "actual" price--what he got paid for it. In other words, at quantity Q, the producer surplus is equal to price minus reserve price. Total producer surplus is the combined area below the horizontal "price" line and above the supply (or MC) curve.

So, to answer your question shortly and succinctly, Economic Profit is the area below price and above the point where average cost intersects the quantity the producer has decided to sell.

Producer Surplus is also the area below price, but it's "southern border" is the MC curve, not the horizontal line of AC.

I hope this makes sense ^^(4 votes)

- What is the difference between $ and $/unit?(1 vote)
- The top graph with $/unit is all about a single
*thing*. For example, the MC curve shows how much extra revenue you get when you sell one more*thing*.

The bottom graph with $ is about*total*money. For example, the TR curve shows the*total*revenue of all of the*things*you sell.(4 votes)

- The Demand curve of monopoly should be upright while in the video, it downward sloping. Like this, are all conclusions of revenue and cost of monopoly still right?(2 votes)
- The demand curve for a monopoly should actually be downward sloping. Someone who claims otherwise is wrong. The demand for a product doesn't change due to the suppliers being a monopoly.(2 votes)

- When Sal draws the ATC curve, he explains why it crosses the MC curve at the lowest point. But why does it crosses the demand curve at the same time?(1 vote)
- it doesn't cross demand curve and MC at the same time here. he just doesn't draw ATC correctly. ATC should cross MC at the lowest point.(3 votes)

- If there is a market that has a monopoly over some sort of a product. What happens to the price of the product when the government taxes the product of the monopoly?(2 votes)
- Prices will increase. If there are substitute products available, consumers will tend to move to the substitute if prices increase too much, or they will stop using the product. So, the relationship is not one-to-one.(1 vote)

- At7:12, when MR and MC meets, the slopes of TC and TR is the same. Does that mean we could find the intercept of MR and MC by finding the quantum where TC and TR have the same slope? Or will that be an unnessesary difficult way to do it? (I haven't had calculus) Is it possible to make a formula for it? Like TC=f(x) and TR=g(x) and they have the same a=slope?(1 vote)
- It actually ends up being more or less the same thing. Marginal revenue = slope of total revenue, marginal cost = slope of total cost. If TC = f(x) and TR = g(x), then MC = f'(x) = slope of f(x) and MR = g'(x) = slope of g(x). The only difference I can think of is that if you already knew the marginal revenue and marginal cost, you wouldn't need to final total cost and total revenue because the marginals ("derivatives" in calculus) are the slopes.(2 votes)

- when dealing with intermediate micro, why is profit drawn as a parabolic shape below total revenue ?(1 vote)
- There will always be a point of maximum profit. Any quantity greater or less than that point will yield lower profits. If you graphed it, it would appear generally likely a negative (upside-down) parabola (though it is in no way guaranteed to be parabolic in the true sense of the term).(2 votes)

- I think the MC curve intersects the ATC curve at ATC(min)?(1 vote)
- Yes, it has to. This is because when ATC is at a minimum, that means that TC is increasing just by the ATC for the next unit, and that rate is just the MC.(2 votes)

## Video transcript

- [Instructor] What I
want to do in this video is review a little bit
of what we've learned about monopolies and, in the process, get a better understanding for some of the graphical representations, which we have talked about in the past, but I wanna put it all
together in this video here. So let's say that the
industry that we are in, the demand curve looks
something like that. That is demand and I'm going to assume that it is a linear demand curve. This axis right here is dollars per unit. In the context of demand, that's price, and this is quantity over here. This little graph here,
we still have quantity in the horizontal axis, but the vertical axis isn't
just dollars per unit, it's absolute level of dollars. Over here we can actually plot total revenue as a function
of quantity, total revenue. Remember, we're assuming
we're the only producer here. We have a monopoly, we have a monopoly in this market. So if we pick a quantity, if we don't produce anything, we're not going to generate any revenue, so our total revenue will be zero. If we produce a bunch, but we
don't charge anything for it, and that's this point right over here, our total revenue will also be zero. We've done this in other videos, but then as we increase
quantity from this point, our total revenue will keep
going up and up and up. There'll be some maximum point and then it'll start going down again, so our total revenue would
look something like this. Total revenue would look something
like that, total revenue. And from the total
revenue, we can think about what the marginal revenue would look like. Remember, the marginal revenue just says if I increase my quantity by a little bit, how much am I increasing my total revenue? So that's essentially the slope, the slope of the total revenue
curve at any given point, or you can think of it as the
slope of the tangent line. We've seen before, when you start here, you have a very high, positive slope and we've seen in other videos it actually ends up being
the exact same value as where the demand curve
intersects the vertical axis right over there, but then it keeps going lower, the slope becomes a little less
deep, less deep, less deep. It's still positive, less deep, less deep, and then it becomes zero right over there and then it starts going negative. It becomes zero right at that quantity. The slope of this keeps
going down and down and down, it's positive, then it becomes zero, and then it actually becomes
negative and you see that here. Now it starts downward
sloping even more steep, even more steep, and even more steep. That's the revenue side of things. Let me label this, this is
our marginal revenue curve, slope of the total revenue. If we're gonna maximize profit, we need to think about
what our costs look like, so let me draw our total cost curve. And I will do it in magenta. Let's say our total costs
look something like this. Total cost looks something like that. Out here, where we have very few units, where we have zero units, all
of our costs are fixed costs. And then as we produce
more and more units, the variable costs start
piling on over there. Even from this diagram, you can actually start to visually see economic profit. Economic profit, and when
we're talking costs and profit in an economics class, like
this is kind of one, I guess, remember, you should view it
in terms of economic profit and when we're talking about total cost, we're talking about opportunity cost. So this is total opportunity cost, both the implicit, both the explicit, the ones that you're actually
paying money for explicitly and the implicit opportunity costs. Total opportunity costs, that's total opportunity cost and the difference between
your total revenue, so for a given quantity,
the difference between your total revenue and your
total opportunity cost, that gives you your economic profit. For this quantity right over here, your economic profit would be represented by the height of this little
bar between these two curves. But what we see what's going on is, as we increase the quantity over here, these curves are getting
further and further apart. That's because the green
curve, the total revenue, it's slope is larger
than this purple curve, which is total opportunity cost, or you could say it total cost. So we could go even further along, just the distance between the two curves gets bigger, bigger,
looks like it maxes out right around here someplace and then the two things start getting closer and closer together. This purple curve's slope is now larger than the orange curve's slope, so then they start getting
closer and closer together. If you were to just look at this graph, whatever the maximum distance between these two things are, it looks like it's about
there, right over here, that would be your
maximum economic profit. But we know we can also visualize it on this curve over here. And we can do that by
plotting our marginal cost. And remember, marginal costs, this is marginal revenue, is the slope of your total revenue curve. Marginal cost is the slope, the instantaneous slope at any point of your total cost curve. So I will do that,
let's do that in yellow. Right over here, you have a zero slope, or pretty close to zero, at least the way I drew it over there. So your marginal cost is going to be pretty close to zero right over there. And then we see this slope
keeps increasing and increasing and increasing and so our
marginal cost will keep increasing, increasing, and increasing, so it will look something like that. That is our marginal cost curve. If we pick a quantity and if we find that the marginal cost over here, I don't know, let's say that
it's five dollars per unit, that literally means that the slope, that that same quantity, the
slope of our total cost curve, that the slope over there
would have to be five. That's what that is telling us. This is plotting the slope of
this curve right over here. And if we want to maximize profit, we already talked about how
you would do it visually on this curve, we can do it over here. Well, right over here, as we produce, if we start from producing
nothing to producing something, for each incremental unit, the incremental revenue we get on that is much higher than the incremental cost. So, hey, we should produce it because we're gonna get profit there. We could keep producing
because we're gonna get profit on each of these incremental units, so we'll keep doing it,
we'll keep doing it, we'll keep doing it,
until the marginal revenue is equal to the marginal cost. At that point, it doesn't make sense for us to produce anymore. If we produce an extra
unit past that point, on that unit our cost will
be higher than our revenue, so what will eat into our economic profit. So this right over here is
where we max the quantity, which we maximize profit. When we see it, we see
it right over there. The way I drew it, luckily, it looks like that is the maximum point
between those two curves as well, and it makes sense. Before this point, when marginal revenue is higher than marginal cost, that means that the slope
of the total revenue curve is larger than the slope
of the total cost curve, so they're getting
further and further apart. After this point, and right at that point their slopes are the same, so the slopes are going to
be the same right over there, and then after that point, the slope of the marginal cost curve, sorry, the marginal cost is high, which tells us the slope of
the total cost curve is higher, than the slope of the total revenue curve. And so they're gonna get
closer and closer together and this distance gets squinched apart. That is where you maximize profit. And if you wanted to
visualize the actual profit, on this graph over here, we cannot obviously visualize it here as the distance between these two curves. If you want to visualize it over here, we would have to plot our
average total cost curve. And essentially, what you're doing is you're just taking this total cost curve and you're not just taking
the slope at any point, that's the marginal cost, instead you're just dividing
it by the quantities. So if you take this total cost curve, you take this value and you divide it by very, very, very low quantity, you're going to get a very,
very, very, very large number. You can imagine, as you're
spreading your fixed costs amongst a very small quantity, so you're gonna get a very large number. Then, as you produce
more and more and more, your average total costs go down, but then your variable
costs start picking up and your average total costs
might look something like that. Average total costs. And so, if you wanna know your profit that you have maximized from
this graph right over here, you say this is the quantity
that maximizes my profit, marginal revenue is
equal to marginal costs, the price that I can get in
the market for that quantity, you go up to your demand
curve and it gives you, this is the price that you
will get for that quantity and so that is, on a per unit basis, that is the revenue that you will get. You can view price is equal to, price is the same thing as revenue, revenue per unit. So on a per unit basis, this
is the revenue you're getting, and on a per unit basis,
this is your average cost, this is average total costs. This is taking all your costs
and dividing it by units. On an average, per unit basis, this is going to be your economic profit. On a per unit basis, and
if you wanted to find your actual economic profit, you would have to multiply it
by the total number of units. So you would, essentially, have the area of this rectangle right over here. This is your per unit
average economic profit and so your total economic profit is going to be quantity
times profit per unit and so this right over
here is economic profit, or maybe I should call it
the total economic profit. Let me write it out, total economic profit. And the area of that rectangle should be the same thing as the height of this right over here. The only reason, and we can maintain this is a sustainable scenario because we have a monopoly. No one else can enter. If this was not a monopoly, if there were no barriers to entry, then other people say hey,
there's economic profit there, that means that there's an incentive for me to put those
same resources together and try to compete
because I'm going to get better returns than my opportunity costs than my alternatives is a
good way to think about it.