Price Elasticity of Demand

Definition

Price Elasticity of Demand (PED) is a measure of the responsiveness or sensitivity of the quantity demanded of a good to changes in its price. It quantifies the percentage change in quantity demanded relative to the percentage change in price.

Formula: $$PED = \frac{\text{Percentage Change in Quantity Demanded}}{\text{Percentage Change in Price}}$$

$$PED = \frac{\Delta Q/Q}{\Delta P/P} = \frac{\Delta Q}{\Delta P} \times \frac{P}{Q}$$

Where:

• ΔQ = Change in quantity demanded
• ΔP = Change in price
• P = Original price
• Q = Original quantity

Types of Price Elasticity of Demand

Price elasticity of demand is classified into five main types based on the coefficient value:

1. Perfectly Elastic Demand (PED = ∞)

• Quantity demanded changes infinitely with even a negligible change in price
• The demand curve is a horizontal line parallel to the quantity axis
• Example: Perfectly competitive market goods

Diagram:

Price
  |
  |     D (horizontal line)
  |___________________
  |
  |_________________ Quantity

2. Elastic Demand (PED > 1)

• Quantity demanded changes by a larger percentage than the percentage change in price
• Consumers are highly responsive to price changes
• The demand curve is relatively flat
• Example: Luxury goods, branded products

Diagram:

Price
  |  \
  |   \  D (relatively flat)
  |    \
  |     \
  |______\_______ Quantity

3. Unit Elastic Demand (PED = 1)

• Percentage change in quantity demanded equals the percentage change in price
• The proportional response is equal
• The demand curve shows a specific slope relationship

Diagram:

Price
  |   \
  |    \  D (unit elastic)
  |     \
  |      \
  |_______\_____ Quantity

4. Inelastic Demand (0 < PED < 1)

• Quantity demanded changes by a smaller percentage than the percentage change in price
• Consumers are less responsive to price changes
• The demand curve is relatively steep
• Example: Essential goods (salt, medicines, basic food items)

Diagram:

Price
  |    \
  |     \  D (relatively steep)
  |      \
  |       \
  |________\__ Quantity

5. Perfectly Inelastic Demand (PED = 0)

• Quantity demanded does not change regardless of price changes
• Consumers are completely unresponsive to price changes
• The demand curve is a vertical line parallel to the price axis
• Example: Life-saving medicines, insulin for diabetics

Diagram:

Price
  |  D
  |  |
  |  |
  |  |
  |__|_________ Quantity

Summary Table

Practical Significance

Understanding price elasticity helps:

• Businesses determine optimal pricing strategies
• Governments design tax policies
• Economists predict consumer behavior
• Firms maximize revenue based on demand responsiveness

Perfect Competition Market: Price and Output Determination (Short Run)

Definition of Perfect Competition

A perfect competition market is a market structure characterized by the following features:

1. Large number of buyers and sellers - No single firm or buyer can influence market price
2. Homogeneous product - All firms produce identical products with no differentiation
3. Free entry and exit - New firms can enter or existing firms can leave the market without barriers
4. Perfect information - All buyers and sellers have complete knowledge of prices and market conditions
5. Price taker - Individual firms cannot set prices; they accept the market price
6. Perfect mobility of factors - Resources can move freely between different uses

Price Determination in Short Run

Market Price is determined by:

• Market demand and market supply interact to establish the equilibrium price
• Individual firm has no control over price
• Price is determined at the point where:
  • Market Demand = Market Supply
  • This is the equilibrium price (Pe)

The firm must accept this market price as given and cannot charge more or less.

Output Determination in Short Run

Each firm determines output where:

Marginal Revenue (MR) = Marginal Cost (MC)

Key points:

• In perfect competition: Price = MR = AR (Average Revenue)
• Since P = MR, the firm's demand curve is perfectly elastic (horizontal line)
• The firm maximizes profit by producing where MR = MC
• At this output level (Qe), the firm earns:
  • Supernormal profit if P > AC (Average Cost)
  • Normal profit if P = AC
  • Loss if P < AC (but continues if P > AVC)

Short-run equilibrium: The firm produces output Qe where MR = MC at the market price Pe, maximizing profit or minimizing loss.

Model Answer: Scarcity and Choice

Scarcity

Scarcity is a fundamental economic problem that arises because human wants and needs are unlimited, while the resources available to satisfy them are limited. In other words, we do not have enough resources (time, money, materials, labor, land) to produce everything we desire.

Key points:

• Resources are finite and exhaustible
• Wants are infinite and constantly growing
• This creates a permanent gap between what we want and what we can have
• Scarcity applies to all economies, whether rich or poor

Choice

Choice is the process of selecting one option over another when faced with limited resources. Because of scarcity, every individual, business, and society must make choices about:

• What to produce
• How to produce it
• For whom to produce it

Key aspects:

• Every choice involves a trade-off - gaining something means giving up something else
• The next best alternative foregone is called the opportunity cost
• Rational decision-making requires comparing benefits and costs of different options

Relationship Between Scarcity and Choice

Scarcity creates the necessity for choice. Without scarcity, there would be no need to choose - we could have everything we want. Because resources are limited:

• Individuals must choose how to spend their income
• Producers must choose which goods to manufacture
• Governments must allocate public resources efficiently

Conclusion

Scarcity and choice are interconnected concepts that form the foundation of economics. They explain why economic problems exist and why efficient resource allocation is essential for all societies.

Model Answer: Budget Line and Consumer Equilibrium

Step 1: Given Data

• Fixed Income, $M = Rs.\ 2000$
• Price of Good X, $P_x = Rs.\ 400$
• Price of Good Y, $P_y = Rs.\ 200$
• Condition (part b): entire budget allocated equally on X and Y

Step 2: Solution

a. Derivation of the Budget Line

The budget line shows all combinations of X and Y purchasable with the full income:

$$M = P_x \cdot X + P_y \cdot Y$$

Substituting values:

$$2000 = 400X + 200Y$$

Dividing throughout by 200:

$$2X + Y = 10$$

Rearranging into slope-intercept form:

$$Y = 10 - 2X$$

Intercepts:

• X-intercept (set $Y = 0$): $X = \dfrac{2000}{400} = 5$ units, point $(5, 0)$
• Y-intercept (set $X = 0$): $Y = \dfrac{2000}{200} = 10$ units, point $(0, 10)$

Slope of budget line $= -\dfrac{P_x}{P_y} = -\dfrac{400}{200} = -2$

The budget line is the straight line joining $(5, 0)$ and $(0, 10)$.

Y
10 |*
   | \
 8 |  \
   |   \
 6 |    \
   |     \  (equilibrium: X=2.5, Y=5)
 5 |------o
   |      |\
   |      | \
   |      |  \
 0 |______|___*____ X
   0     2.5   5

b. Equilibrium Point with Equal Budget Allocation

The consumer spends the budget equally, so:

$$\text{Spent on X} = \text{Spent on Y} = \frac{2000}{2} = Rs.\ 1000$$

Quantities purchased:

$$X = \frac{1000}{P_x} = \frac{1000}{400} = 2.5 \text{ units}$$

$$Y = \frac{1000}{P_y} = \frac{1000}{200} = 5 \text{ units}$$

Equilibrium combination: $(X, Y) = (2.5,\ 5)$

Verification (point must lie on budget line):

$$400(2.5) + 200(5) = 1000 + 1000 = 2000 \checkmark$$

Since $400X + 200Y = 2000$ is satisfied, the point $(2.5, 5)$ lies on the budget line and represents the consumer's chosen equilibrium when income is divided equally between the two goods.

Note: Strictly, consumer equilibrium requires the tangency condition $MRS_{xy} = \dfrac{P_x}{P_y}$ using an indifference curve. Since no utility function is provided, the problem defines the equilibrium purely by the equal-allocation condition, giving $(2.5, 5)$.

Model Answer: Instruments of Monetary Policy [5 marks]

Monetary policy instruments are the tools used by the central bank to control the money supply, credit availability, and interest rates in the economy. The main instruments are:

1. Open Market Operations (OMO)

• Purchase and sale of government securities (bonds, treasury bills) in the open market
• When the central bank buys securities, money supply increases
• When it sells securities, money supply decreases
• Most flexible and frequently used instrument

2. Bank Rate (Discount Rate)

• The interest rate at which the central bank lends to commercial banks
• Increase in bank rate discourages borrowing, reducing money supply
• Decrease in bank rate encourages borrowing, increasing money supply

3. Reserve Requirement Ratio (RRR) / Cash Reserve Ratio (CRR)

• The percentage of deposits that commercial banks must keep as reserves with the central bank
• Increase in CRR reduces lending capacity of banks, decreasing money supply
• Decrease in CRR increases lending capacity, increasing money supply

4. Statutory Liquidity Ratio (SLR)

• The percentage of deposits that banks must invest in government securities
• Increase in SLR reduces funds available for lending
• Decrease in SLR increases credit availability

5. Moral Suasion

• Persuasive measures and guidelines issued by the central bank to commercial banks
• Requests to follow lending policies aligned with economic objectives
• Non-binding but influential

Note: These are standard monetary policy instruments used by central banks globally. The reference notes were unavailable; this answer reflects universally accepted economic principles in monetary policy.