1. Law of EquiMarginal UtilityBy
BALAJI KANNAN

2. Law of Equi Marginal Utility Maximum satisfaction out of the expenditure of a given sum can be obtained if the utility derived from the last unit of money spent on each object of expenditure is, more or less the same. Illustration:- Suppose a man goes to the market with Rs.400 in his pocket, which is want to spend on oranges, grapes and Banana, and further. Suppose that the utility he expects to derive from each unit of Rs.25 spent on these commodities is follows.

3. The Equi Marginal Principle
The optimum amount of two alternatives consumed (or produced)will be where the marginal benefit ratios of the two alternatives are equal to their marginal cost ratios :
MBa MCa =
MBb MCb

4. To see the sense of this,say that the last unit of Apple you consumed gave three times as much utility as the last unit of Orange.Yet Apple only cost twice as much as Orange. Thus ,a consumer gain by increasing the consumption of Apple thereby reducing orange.At one point of time the same consumer start shifting to consume orange since he gained maximum satisfaction in consuming Apple(Applying Law of DMU) Now the MU of apple falls and results in increase of MU of Orange.This subsitution process continues till MU of Apple = MU of Orange also with the same price.

5. Utility derived from the Rs.25 spent on
Rs25/unit
Utility derived from the Rs.25 spent on
Oranges
Grapes
Banana
1St 10 13 11
2nd 8 12 9
3rd 7 6
4rth 5
5th 4
6th 3 2
7th 1

6. The purchaser will spend the first 25 on the object, which will give him the greatest satisfaction. In this case such an article is Grapes, the utility of its first unit is 13, which is maximum.
Guided by the same motive, he will spend the second Rs. 25 on Grapes. He will spend the third Rs. 25 on Banana and the forth-on oranges. In this way he will go spending money. The following table indicates the order in which he will spend the Rs.400 he has got with him.

7. Rs.25
Object of expenditure
Utility derived
1St
Grapes 13
2nd 12
3rd
Banana 11
4rth
Orange 10
5th
6th 9
7th 3
8th 8
9th 7
10th 6
11th
12th 5
13th
14th 4
15th
16th

8. Total utility derived from Rs. 400 out off 117
The above table shows that he will spend Rs. 25 each 5 on oranges, 6 on Grapes, and 5 on Banana , and will in total derive 117 units of utility. This is the maximum satisfaction that he can obtain out of his expenditure. If he does not follow this scheme of expenditure, he will not be able to derive maximum total utility.
Therefore, if we want to derive maximum satisfaction out of our expenditure, we should spend our money in such a way as to derive, more or less, the same satisfaction from the last unit of money spends on each head. This is the law of Equimarginal utility.

9. Some Definitions Total Utility:
The total satisfaction a consumer gets from the consumption of all units of a good consumed within a given time period
Marginal Utility:
The extra satisfaction gained from consuming one extra unit of a good within a time period
Util:
An imaginary unit of satisfaction derived from the consumption fo a good

10. Law of Diminishing Marginal Utility
Principal of Diminishing Marginal Utility:
The more of a product a person consumes ,the less will be the additional utility gained from one more unit. Or
As more units of a good are consumed,additional units will provide less additional satisfaction than previous units.

11. MU from consuming biscuits
Biscuit Packets Consumed
TU in Utils
MU in utils - 1 7 2 11 4 3 13 14 5 6 -1

12. Using Calculus to derive the MU Function
A consumer’s typical utility function for a good might be of the form:
TU=60Q-4Q²
Where Q is the quantity of the goods consumed
Tabulate by constructing a table for TU
Marginal Utility is the first derivative of total utility
dTU
MU= =60 -8Q dQ

13. Problem for Practice
Derive the MU function from the following TU function:
TU = 200Q-25Q²+Q³
From this MU Function ,draw up a table upto the level of Q where MU becomes negative .Graph these figures.

14. Marginal Consumer Surplus(MCS)
It is the difference between what you are willing to pay for one more unit of a good and what you are actually charged .
For Eg If A is prepared to pay Rs 25 for a Biscuit packet which actually costs him Rs 20,then Rs 5 will be called as Marginal Consumer Surplus(MCS)

15. Total Consumer Surplus(TCS)
It is the difference between the total utility from all the units and your expenditure on them.
TCS = TU - TE

16. Marginal Utility and the demand curve of the good
The price elasticity of demand will reflect the rate at which MU diminishes.
If there are close substitutes for a good,it is likely to have an elastic demand,and its MU will diminish slowly as consumption increases.
It is likely that the MU of money diminishes as income rises.

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