Market demand

Detail

1. What market demand means

• Individual demand: how much one consumer wants to buy at each price, with other things (income, tastes, prices of other goods) unchanged.
• Market demand: the total quantity demanded by all consumers in the market at each price.
• Market demand curve: a graph of this total. It shows, for every price, how much the whole market will buy.
• It is built by horizontal summation:
• Pick a price. Read off each person's quantity. Add the quantities.
• Quantity sits on the horizontal axis (x-axis), so we add along that axis.

• Prices are never added. Every buyer faces the same market price.

• Formula: Q_market(p) = q₁(p) + q₂(p) + … + qₙ(p), where qᵢ(p) is buyer i's demand at price p.

2. Class 9 table (Table 9.1): adding up quantities

Price	Srivalli	Alex	Israt	Market demand
₹150	1 kg	2 kg	3 kg	6 kg
₹100	2 kg	4 kg	6 kg	12 kg
₹50	3 kg	6 kg	9 kg	18 kg

• At ₹100: 2 + 4 + 6 = 12 kg. The price stays ₹100. It does not become ₹300.
• Each person's curve slopes downward, so the market curve slopes downward too. This is the law of demand for the market: price down → quantity demanded up.

3. Adding linear demands (Class 12): the kinked curve

• Linear demand: a demand curve that is a straight line, written q = a − bp.
• a = quantity bought when price is zero.

• b = how many units demand falls for each ₹1 rise in price.

• Consumer 1: d₁(p) = 10 − p. This becomes zero above ₹10. At that price consumer 1 stops buying.

• Consumer 2: d₂(p) = 15 − p. This becomes zero above ₹15.
• Market demand, step by step:
• p ≤ 10 → both buy → (10 − p) + (15 − p) = 25 − 2p
• 10 < p ≤ 15 → only consumer 2 buys → 15 − p

• p > 15 → nobody buys → 0

• Kink: a sharp bend in the curve. Here it is at p = 10, q = 5.

• Check: 25 − 2(10) = 5, and 15 − 10 = 5. Both pieces meet at the same point.

• Above ₹10 the curve is steeper (slope −1). Below ₹10 it is flatter (slope −2 in q terms), because two buyers now respond to price.

• Rule: at each price, add only the consumers who actually buy at that price.

• Common mistake: writing 25 − 2p for every price. At p = 12 this gives 1. The correct answer is 15 − 12 = 3. At p = 12, consumer 1's "10 − 12 = −2" must be counted as zero. Negative quantities do not exist.

• Worked numbers:

• p = 4 → 25 − 8 = 17 (6 + 11)
• p = 12 → 3 (0 + 3)
• p = 16 → 0

4. Identical consumers

• If there are n identical consumers (same demand function), market demand = n × individual demand.
• Class 12 exercise: 20 consumers, each with d(p) = 10 − 3p.
• Market demand = 20 × (10 − 3p) = 200 − 60p for p ≤ 10/3 (about ₹3.33).
• 0 for p > 10/3, because at that price each person's demand hits zero.

• Check at p = 2: one person buys 10 − 6 = 4. The market buys 20 × 4 = 80 (= 200 − 120).

• The price at which demand becomes zero (the choke price) is the same for the market and for one person, because everyone is identical. So there is no kink.

5. Other drills

• Class 12 table exercise: add d₁ and d₂ at each price.
• p = 1: 9 + 24 = 33

• p = 6: 4 + 12 = 16

• Unequal cut-off prices: d₁ = 20 − p (buys up to ₹20); d₂ = 30 − 2p (buys up to ₹15).

• p ≤ 15 → both buy → (20 − p) + (30 − 2p) = 50 − 3p
• 15 < p ≤ 20 → only consumer 1 buys → 20 − p
• p > 20 → 0

• The kink is at p = 15, q = 5 (50 − 45 = 5; 20 − 15 = 5).

• Exam method:

• Find each buyer's cut-off price.
• Split the price axis at those cut-offs.
• In each price range, add only the active buyers.

6. Number of buyers: a determinant of market demand

• Determinant: a factor other than the good's own price that decides how much is demanded. For one person these are income, tastes, and the prices of related goods. Market demand adds one more: the number of buyers.
• More buyers → the market curve shifts right, even if each person's demand does not change:
• Population grows, or new markets open, or online selling reaches new areas.
• At every price, more people are buying.

• So a larger quantity is demanded at every price. This is a shift of the curve, not a movement along it.

• Standard theory lists the number of consumers in the market as a factor that shifts the demand curve [2].

• Indian examples of a growing buyer base:
• India's population is projected at about 142.6 crore (1,425.9 million) in 2026, with about 92.4 crore (923.9 million) of working age (15–59). These figures come from the Technical Group on Population Projections, 2011–2036 (July 2020) [3].
• India had 101.78 crore internet subscribers as of 30 September 2025: 42.77 crore rural and 59.01 crore urban [4].
• 98.09% of villages have internet access [4].

• Every new online buyer is one more "qᵢ" in the horizontal sum. So e-commerce reach pushes market demand for many goods to the right.

• Movement vs shift:

• Own price changes → movement along the market curve.
• Number of buyers, income, tastes or related prices change → shift of the whole market curve.

7. NCERT error: the Class 9 "Don't miss out" box

• What Class 9 says: the market curve is flatter than each person's curve, so the market is "more responsive" to price.
• Why this is wrong: it mixes up slope with elasticity.
• Slope = change in quantity for a given change in price, in absolute units (kg per ₹). The market curve is flatter only because its quantities are bigger. From ₹150 to ₹50 the market changes by 12 kg (6 → 18), while Srivalli changes by 2 kg (1 → 3).

• Price elasticity of demand (eₚ) = % change in quantity demanded ÷ % change in price. It uses percentage changes, so the size of the units does not matter.

• Proof from Table 9.1:

• Market demand is exactly 6 × Srivalli's demand at every price (6 = 6×1, 12 = 6×2, 18 = 6×3).
• ₹150 → ₹50: Srivalli goes 1 → 3 kg (+200%). The market goes 6 → 18 kg (+200%).
• The price change is the same for both (−66.7%).

• So eₚ is the same for the market and for Srivalli.

• General rule: if the market is just k × one person's demand, the market elasticity equals the individual elasticity at every price. Multiplying by k changes the slope but not the percentage changes.

• When buyers differ, market elasticity is a weighted average (an extension of the Class 12 example):
• At p = 5 in section 3: consumer 1 buys 5, with eₚ = −1 × 5/5 = −1. Consumer 2 buys 10, with eₚ = −1 × 5/10 = −0.5.
• Market: q = 15, eₚ = −2 × 5/15 = −0.67.
• Weighted by each buyer's share of quantity: (5/15)(−1) + (10/15)(−0.5) = −0.67. The two answers match.
• So the market is not automatically more elastic than its members. Its elasticity lies between theirs.

Prelims Hooks

• Market demand = horizontal summation of individual demand curves. Quantities are added at a given price. Prices are never added.
• n identical consumers → market demand = n × individual demand. For example, 20 × (10 − 3p) = 200 − 60p, which becomes zero above p = 10/3.
• d₁ = 10 − p and d₂ = 15 − p give market demand 25 − 2p (p ≤ 10), 15 − p (10 < p ≤ 15) and 0 (p > 15). The kink is at p = 10, q = 5.
• A kink appears only when buyers have different cut-off (choke) prices. Identical buyers give a curve with no kink.
• Number of buyers is a determinant of market demand but not of individual demand. A rise in it shifts the curve right.
• Trap: "a flatter market demand curve means the market is more price-elastic." This is false. Slope ≠ elasticity. When market demand = k × individual demand, elasticities are identical (e.g. +200% for both in Table 9.1).
• Market price elasticity is the quantity-weighted average of individual elasticities at that price.
• India: 101.78 crore internet subscribers (30 Sept 2025), of which 42.77 crore are rural [4]. Projected population 1,425.9 million (2026) [3].

Mains Points

• Demographic dividend and the size of the market (GS-III):
• About 92.4 crore people of working age are projected for 2026 [3].

• More earning buyers → the market demand curve shifts right → firms can produce at scale → a case for jobs-led growth that turns population into purchasing power.

• Digital reach widens markets (GS-III, inclusive growth):

• 42.77 crore rural internet users (Sept 2025) [4] and platforms such as ONDC and e-Saras bring new buyers into national markets.

• This raises market demand without raising any single person's demand. It helps small sellers, but only if last-mile delivery and digital literacy improve too.

• Policy design must use elasticity, not slope:

• To judge how a tax or subsidy will change consumption (e.g. GST rate changes, fuel price changes), policymakers need the percentage response of different buyer groups.

• Market elasticity is a weighted average, so a price change can hurt low-income, price-sensitive groups a lot even when total demand looks "inelastic". This is an argument for targeted transfers.

• Kinked market demand in real markets:

• When prices rise past what poorer households can pay, whole groups of buyers leave the market (the kink).
• This explains sharp drops in demand for items like LPG refills or pulses when prices spike. It supports price-band schemes such as PMUY subsidies and buffer-stock releases.