NSS Economics

Effective Teaching & Learning Strategies Workshop

Topic: Law of Diminishing Marginal Return

Developmental Stage:

[Objective: Read numerical data in a table, Clarify the relationship between fixed factor, variable factor & total product]

Task 1: Read the data of the following table and answer the questions

Machine / Labour / Total No. of Sports Shoes
1 / 1 / 15
1 / 2 / 40
1 / 3 / 69
1 / 4 / 80
1 / 5 / 90

1.  What are the inputs in this production?

2.  What is the output in this production? How do we describe this output level in Economic term?

3.  Which item belongs to fixed factor? Which one is variable factor?

4.  Try to describe the following Input-Output relationship:

i.  The relationship between the total product and fixed factor.

ii.  The relationship between the total product and variable factor.

iii.  Does the total product change at the same rate? Please give evidence to support your answer.

5.  The firm is now in short-run or long-run production period? Why?

[Objective: Calculation of TP & AP, clarify the concept of AP]

Task 2: Fill in the missing figures for average product and total product

Machine / Labour / Total Product (TP) / Average Product (AP)
4 / 1 / 120
4 / 2 / 250
4 / 3 / 420 / 140
4 / 4 / 540
4 / 5 / 120

1.  Which of the following statements do you think is the correct definition of Average Product?

Statement 1: ‘Average Product is the amount of output per unit of a fixed factor employed.’

Statement 2: ‘Average Product is the amount of output per unit of a variable factor employed.’

2.  Can you write down the formula of Average Product?

AP = ------

[Objective: Assessing students’ understanding in the previous stages]

Quiz: Fill in the missing figures in the following table

Variable Factor / Fixed Factor / Total Product (TP) / Average Product (AP)
7 / 10 / 70 / ______
8 / 10 / 88 / ______
9 / ______/ ______/ 13
10 / 10 / 150 / ______
11 / ______/ 18
12 / 10 / 216 / ______
… / … / … / …
______/ ______/ 240 / 12

[Objective: Calculation of MP, clarify the concept of MP]

Task 3: Fill in the missing figures for average product and marginal product

Machine / Labour / Total Product
(TP) / Average Product (AP) / Marginal Product (MP)
4 / 1 / 20
4 / 2 / 44
4 / 3 / 72
4 / 4 / 105
4 / 5 / 143
4 / 6 / 173
4 / 7 / 195
4 / 8 / 210
4 / 9 / 220
4 / 10 / 213

1.  How do you describe the changes of marginal product?

2.  From which unit of labour, the marginal product begins to decrease?

3.  Can you think of some reasons in explaining the changes of MP?

4.  State the law of diminishing marginal returns.

5.  Explain whether the above data illustrate the law.

Scaffolding Strategy:
CHECKLIST OF THE STEPS:
a. Identify the KEY data in the table.
(i) factors of production (e.g. Capital & Labour)
(ii) given output level (TP / AP / MP)
b. Identify the variable / fixed factors.
(i) Capital à The number is ‘fixed’ / ‘increasing’ / ‘variable’?
(ii) Labour à The number is ‘fixed’ / ‘increasing’ / ‘variable’?
c. What ‘run’ is it?
d. Identify the changes in MP.
(i) Convert the given data into MP:
- Given TPà MP
- Given APàTPàMP
(ii) Describe the changes of MP with the changes of variable factors.
e. Making judgment: explain whether the data illustrate the law.
Criteria:
(i) Is it in short-run production period?
(ii) Does the MP eventually decrease when more and more variable factors are added to the production?

Further Discussion / Challenging Questions:

1.  If you are the owner of the firm, will you employ the labour if his/her MP is a negative number?

2.  How about if his/her MP is a positive number? Is it a ‘MUST’ condition for us to employ him/her? What other factors do we need to consider?


Motivation by examination:

Adding varieties by providing students more exercises & more discussion through group work.

Anchoring Exercise:

Level 1: Simplest Example

The table below shows the production of a firm.

Machinery / Labour / Total Product
3 / 1 / 20
3 / 2 / 45
3 / 3 / 75
3 / 4 / 90
3 / 5 / 100

Explain whether the above data illustrate the law of diminishing marginal returns.

Suggested Answer:

The law of diminishing marginal returns states that in the ______run, as more and more ______factors are added to a certain quantity of ______factors, the ______product will eventually ______, holding ______.

The following data are derived from the table given in the question:

Machinery / Labour / Total Product / Marginal Product
3 / 1 / 20
3 / 2 / 45
3 / 3 / 75
3 / 4 / 90
3 / 5 / 100

The above data ______illustrate the law of diminishing marginal returns.

As shown in the table, machinery is a ______factor and labour is a ______factor in its production; the firm is operating in the ______run.

Given the quantity of ______is fixed, when the ____-th unit of labour is added, the marginal product of labour starts to decrease from _____units to _____units, which illustrates the law of diminishing marginal returns.

Level 2: Non-Example

Machinery / Labour / Total Product
1 / 1 / 20
2 / 2 / 45
3 / 3 / 75
4 / 4 / 90
5 / 5 / 100

Explain which law in economics can be illustrated by the above data.

Suggested Answer:

a.  Define the economic law.

______

b.  The firm is operating in short run or long run, why?

______

c.  Explain whether the above data illustrate the law in (a).

______

______

Level 3: More Complex question

No. of workers / No. of working hours per worker / Machines (Units) / Average Product
10 / 11 / 3 / 20
10 / 10 / 3 / 45
10 / 9 / 3 / 75
10 / 8 / 3 / 90
10 / 7 / 3 / 100

Explain whether the above data illustrate the law of diminishing marginal returns.

______

______

______

______

©HKETA (2009) P.1