Class 9 Social Science – The Price Puzzle | Original Visual Revision Notes

📝 Section 1 — Classroom Notes

1.1 What Is Demand?

Demand means how much people want to buy.
It depends on the price of goods.
More money means people can buy more.
Demand changes when tastes change too.
It is always about willing buyers.
People choose what they need most first.
Demand is not the same as a wish.
You must have money to create demand.

1.2 Law of Demand

Price goes up, demand goes down.
Price goes down, demand goes up.
This always works when other things stay same.
People buy less when things cost more.
This rule is called the law of demand.
Cheap things attract more buyers always.
This is a basic rule of economics.

1.3 The Demand Curve

A demand curve is a line on a graph.
It slopes downward from left to right.
Price is shown on the up-down side.
Quantity is shown on the flat side.
The line shows how demand changes with price.
Each dot on the line is one price-quantity pair.
We can read the graph to find demand.

1.4 What Is Supply?

Supply means how much sellers want to sell.
Sellers make goods and bring to market.
They decide how much to offer.
Supply depends on cost of making goods.
More sellers means more supply in market.
Farmers, shops, and factories all supply goods.
Supply is about what is ready for sale.

1.5 Law of Supply

Price goes up, supply goes up too.
Sellers want to sell more at high price.
Price goes down, sellers offer less.
This is the law of supply.
It works when other things stay same.
High price gives sellers more profit.

1.6 The Supply Curve

A supply curve is a line on graph.
It slopes upward from left to right.
Higher price means more goods are offered.
The curve shows supply at each price.
Price is on left side of graph.
Quantity is on the bottom of graph.
We can read supply for any price.

1.7 Market Balance Point

Balance happens when demand equals supply.
This point is called market equilibrium.
At this price, all goods get sold.
No extra goods are left over.
The market is happy at this price.
Both buyers and sellers agree on price.
This is the best price for everyone.

1.8 Things That Change Demand

Income of people can change demand.
If people earn more, they buy more.
Change in taste can shift demand too.
Price of related goods affects demand.
More people in town means more demand.
Fashion trends also change what people want.
Festivals and seasons can push demand up.
Ads on TV can also increase demand.

1.9 Things That Change Supply

Better machines help make more goods faster.
New technology can increase supply a lot.
If raw materials cost more, supply drops.
More factories means more goods are made.
Good weather helps farmers grow more crops.
Bad weather can reduce supply of food.
Government rules can also change supply.

1.10 Government Steps In

Government can set a maximum price.
This is called a price ceiling.
It keeps prices low for poor people.
Government can also set a minimum price.
This is called a price floor.
Price floor helps sellers earn enough money.
These rules control the market prices.

✏️ Section 3 — Worked Examples

Q1: Apples cost 50 rupees per kg. Price rises to 80. What happens to demand?

Step 1: Old price of apples = 50 rupees.

Step 2: New price of apples = 80 rupees.

Step 3: Price went up by 30 rupees.

Step 4: Use the law of demand here.

Step 5: Price up means demand goes down.

Answer: Demand for apples will go down.

Q2: A new factory opens making shoes. What happens to supply of shoes?

Step 1: Before, fewer factories made shoes.

Step 2: Now one more factory opens up.

Step 3: More shoes can be made now.

Step 4: More sellers means more supply.

Step 5: Supply curve shifts to the right.

Answer: Supply of shoes will go up.

Q3: At 20 rupees, demand is 100 and supply is 100. Is this equilibrium?

Step 1: Demand at this price = 100 units.

Step 2: Supply at this price = 100 units.

Step 3: Check: is demand equal to supply?

Step 4: Yes, 100 = 100, they are equal.

Step 5: Equal demand and supply = equilibrium.

Answer: Yes, 20 rupees is the equilibrium price.

📋 Section 4 — Cheat Sheet

Word	Meaning
Demand	How much people want to buy.
Supply	How much sellers want to sell.
Price	How much money a good costs.
Law of Demand	Price up means demand goes down.
Law of Supply	Price up means supply goes up.
Demand Curve	A line that slopes downward on graph.
Supply Curve	A line that slopes upward on graph.
Equilibrium	Where demand and supply are equal.
Market	Place where buyers and sellers meet.
Price Ceiling	Highest price the government allows.
Price Floor	Lowest price the government allows.
Income	Money that people earn from work.
Technology	Machines and tools that help make goods.
Quantity	The number or amount of goods.

📄 Section 5 — Take-Home Handout

Part A: Fill in the Blanks

1. Demand means how much people want to _____.
2. When price goes up, demand goes _____.
3. The demand curve slopes _____.
4. Supply means how much sellers want to _____.
5. When price goes up, supply goes _____.
6. The supply curve slopes _____.
7. Balance of demand and supply is called _____.

Part B: True or False

1. Price up means demand up. ( _____ )
2. Supply curve slopes upward. ( _____ )
3. Equilibrium means demand equals supply. ( _____ )
4. Price floor is the highest price. ( _____ )
5. More factories means less supply. ( _____ )
6. Demand curve slopes downward. ( _____ )
7. Government sets price controls. ( _____ )

Part C: Match the Columns

Column A	Column B
1. Demand curve	a. Price up, supply up
2. Supply curve	b. Where demand = supply
3. Law of supply	c. Slopes downward
4. Equilibrium	d. Maximum price by govt
5. Price ceiling	e. Slopes upward

Part D: One Word Answers

1. What goes down when price goes up? _____
2. What type of curve slopes upward? _____
3. Where do buyers and sellers meet? _____
4. What does government set as lowest price? _____
5. What helps factories make more goods? _____
6. What is the balance point called? _____

Part E: Think and Answer

1. Why do people buy less when price goes up?
2. What happens when a new factory opens?
3. Why does the government set price controls?
4. What happens at the equilibrium price?
5. Name two things that change demand.
6. Name two things that change supply.
7. Draw a demand curve and label it.

Part F: Answer Key for Teacher

A: 1-buy, 2-down, 3-downward, 4-sell, 5-up, 6-upward, 7-equilibrium
B: 1-False, 2-True, 3-True, 4-False, 5-False, 6-True, 7-True
C: 1-c, 2-e, 3-a, 4-b, 5-d
D: 1-Demand, 2-Supply, 3-Market, 4-Price floor, 5-Technology, 6-Equilibrium

🃏 Section 6 — Revision Flashcards

What is demand?

How much people want to buy.

What is supply?

How much sellers want to sell.

Law of Demand?

Price up, demand goes down.

Law of Supply?

Price up, supply goes up.

Demand curve shape?

It slopes downward left to right.

Supply curve shape?

It slopes upward left to right.

What is equilibrium?

When demand and supply are equal.

What is a price ceiling?

Highest price the government allows.

What is a price floor?

Lowest price the government allows.

What shifts demand?

Income, taste, and population changes.

What shifts supply?

Technology, cost, and number of sellers.

What is a market?

Place where buyers and sellers meet.

✅ Detailed Answers — Take-Home Handout

Part A: Fill in the Blanks — Answers

1. buy (demand = how much buyers want to buy at a given price)
2. down (Law of Demand: when price rises, quantity demanded falls)
3. downward (the demand curve slopes from upper-left to lower-right)
4. sell (supply = how much sellers want to sell at a given price)
5. up (Law of Supply: when price rises, sellers are willing to supply more)
6. upward (the supply curve slopes from lower-left to upper-right)
7. equilibrium (the point where quantity demanded equals quantity supplied)

Part B: True or False — Answers

1. False — Price going UP means demand goes down. This is the Law of Demand — price and demand move in opposite directions.
2. True — The supply curve slopes upward because higher prices motivate sellers to produce and supply more goods.
3. True — Equilibrium is the balance point where quantity demanded equals quantity supplied and the market clears.
4. False — A price floor is the minimum (lowest) price set by the government — e.g., minimum support price (MSP) for farmers. A price ceiling is the maximum price.
5. False — More factories mean more supply, not less. When more producers enter the market, the total supply of goods increases.
6. True — The demand curve slopes downward — as price falls, consumers buy more; as price rises, they buy less.
7. True — Government sets price controls like price ceilings (maximum price) to protect consumers, and price floors (minimum price) to protect producers.

Part C: Match the Columns — Answers

1 → c (Demand curve — Slopes downward)
2 → e (Supply curve — Slopes upward)
3 → a (Law of supply — Price up, supply up)
4 → b (Equilibrium — Where demand = supply)
5 → d (Price ceiling — Maximum price set by government to protect consumers)

Part D: One Word Answers — Answers

1. Demand (demand falls when price rises)
2. Supply curve (the supply curve slopes upward)
3. Market (buyers and sellers meet in a market)
4. Price floor (the minimum price set by government)
5. Technology (better technology helps factories make more goods efficiently)
6. Equilibrium (the balance point is called market equilibrium)

Part E: Think and Answer — Answers

Why do prices of vegetables rise in summer? In summer, heat reduces crop yields and spoils vegetables quickly. This means supply goes down. At the same time, demand stays the same or goes up (more people want cooling/salad vegetables). When supply falls and demand stays high, prices rise. This is basic demand-supply law in action.

What happens when a new factory opens? A new factory increases supply. When supply increases, the supply curve shifts to the right. At the same equilibrium demand level, this causes prices to fall (good for consumers) and quantity available in the market to increase.

How does equilibrium help the market? At equilibrium, there is no shortage (too little supply) and no surplus (too much supply). Every buyer who wants to buy at the price can find a seller, and every seller who wants to sell can find a buyer. This creates a stable, fair market without waste or shortages.

The Price Puzzle: What Drives the Market