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## PowerPoint Slideshow about '10.7 Marginal Analysis in Business and Economics' - ashley

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The sharp increases may occur when new factories have to be built and when resources become scarce

Cost C

- This is the non-linear cost function.
- It is an increasing function because it costs more if you produce more and more items
- The cost function increases quickly at first and then slowly because producing larger quantities is often more efficient then producing smaller quantities.

Fixed cost

Quantity q

In reality, for a large values of q, the price is dropping

- This is the non-linear revenue function.
- In this section, however, there are problems that we will use linear revenue function
- It is an increasing function because the company receives more money if they sell more and more items

Revenue R

Quantity q

For what production quantities does the company make a profit?

- When revenue function is above cost function
- Production between 150 and 520 items will generate a profit

$$$

R

C

q

150

520

Estimate the maximum profit

- Arrow goes up represent a profit
- Arrow goes down represent a loss
- Maximum Profit can occur where R’=C’

$$$

R

C

q

150

520

Marginal Cost

Remember that marginal refers to an instantaneous rate of change, that is, a derivative.

Definition:

If x is the number of units of a product produced in some time interval, then

Total cost = C(x) for producing x units

Marginal cost = C’(x)

Marginal cost is the instantaneous rate of change of cost relative to a given production level

Marginal Revenue andMarginal Profit

Definition:

If x is the number of units of a product sold in some time interval, then

Total revenue = R(x) for selling x units

Marginal revenue = R’(x)

If x is the number of units of a product produced and sold in some time interval, then

Total profit = P(x) = R(x) – C(x)

Marginal profit = P’(x) = R’(x) – C’(x)

Marginal Cost and Exact Cost

Assume C(x) is the total cost of producing x items. Then the exact cost of producing the (x + 1)st item is

C(x + 1) – C(x).

The marginal cost is an approximation of the exact cost.

C’(x) ≈ C(x + 1) – C(x).

Similar statements are true for revenue and profit.

Application

- The total cost of producing x electric guitars is C(x) = 1,000 + 100x – 0.25x2.
- Find the exact cost of producing the 51st guitar.
- The exact cost is C(x + 1) – C(x).
- C(51) – C(50) = 5,449.75 – 5375 = $74.75.
- Use the marginal cost to approximate the cost of producing the 51st guitar.
- The marginal cost is C’(x) = 100 – 0.5x
- C’(50) = $75.

Example 1:

A company manufactures automatic transmissions for automobiles. The

total weekly cost (in dollars) of producing x transmissions is given by

C(x) = 50000 + 600x -.75x2

(A) Find the marginal cost function

C’(x) = 600 – 1.5x

(B) Find the marginal cost at a production level of 200 transmissions per week

and interpret the results.

C’(200) = 600 -1.5(200) = 600 - 300 = 300

At a production level of 200 transmissions, total costs are increasing at

the rate of $300 per transmission.

(C) Find the exact cost of producing the 201st transmission

C(201) – C(200) = 140299.25 – 140000= 299.25

Example 2:

Price-demand equation: x = 10000 -1000 p or p = 10 - .001x

where x is the demand at price p (or x is the number of headphones

retailers are likely to buy at $p per set).

Cost function:C(x) = 7000 + 2x

where $7000 is the fixed costs and $2 is the estimate of variable costs per

headphone set (materials, labor, marketing, transportation, storage, etc.)

- Find the domain of the function defined by the price-demand equation.

p = 10 - .001x ≥ 0; -.001x ≥ -10; so 0 ≤ x ≤ 10,000

(B) Find the marginal cost function C’(x) and interpret.

C’(x) = 2 means it costs an addition $2 to produce one more headset

(C) Find the revenue function (R = xp) as a function of x, and find its domain.

R = xp = x(10 - .001x) = 10x - .001x2

Domain: x(10 - .001x) ≥ 0; so 0 ≤ x ≤ 10,000

(D) Find the marginal revenue at x = 2000, 5000, and 7000. Interpret the results

Use G.C or find R’(x), R’(2000) = 6; revenue is increasing at $6/headphone

R’(5000) = 0; revenue stays the same with an increase in production

R’(7000)= -4; revenue is decreasing with an increase in production

continue

(E) Graph the cost function and the revenue function in the same coordinate system, find the intersection points of these two graphs, and interpret the results.

R(x) = 10x - .001x2

C(x) = 7000 + 2x

G.C window: -10,10000,-10,30000

To find the intersections using GC:

you can trace the cursor or press

2nd trace, 5, enter, enter, then move

the cursor to the intersection, then

press enter again. You can also

Solve algebraically, set R=C

C

R

Break-even-points:

points where revenues and costs are the same. In this

problem, they are: (1000, 9000) and (7000, 21000)

continue

Maximum point

(F) Find the profit function, and sketch its graph.

R(x) = 10x - .001x2

C(x) = 7000 + 2x

P(x) = R(x) – C(x)

P(x) = -.001x2 + 8x – 7000

Use GC to find the production level to maximize the profit:

2nd, Trace, 4, move cursor to the left, press enter, move cursor to the right, press enter, move to the maximum point then press enter again. You should get 4000

(G) Find the marginal profit at x = 1000, 4000, and 6000. Interpret these results.

P’(x) = -.002x + 8

P’(1000) = 6 profit is increasing if produce more

P’(4000) = 0 profit stays the same if produce one more

P’(6000) = -4 profit is decreasing if produce more

Marginal Average Cost

Definition:

If x is the number of units of a product produced in some time interval, then

Average cost per unit =

Marginal average cost =

Marginal Average Revenue Marginal Average Profit

If x is the number of units of a product sold in some time interval, then

Average revenue per unit = Marginal average revenue =

If x is the number of units of a product produced and sold in some time interval, then

Average profit per unit =

Marginal average profit =

Example 3:

The cost function for the production of headphone sets :

C(x) = 7000 + 2x

- Find C(x) and C’ (x)
- Find C(100) and C’(100) and interpret

C(100) = 72; the average cost per headphone is $72

C’(100) = -0.70; the average cost is decreasing at a rate of 70 cents

per headphone

- Use the result in part B to estimate the average cost per headphone at a production level of 101 headphone sets.

72 – 0.7 = 71.30; about $71.30 per headphone

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