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Fundamental Economic Concepts

Master scarcity, opportunity cost, incentives, supply and demand, price controls, comparative advantage, and economic systems.

Practice this skill 20 min Fundamental economic concepts Leer en español
Key idea

What you'll learn

In plain words: Economics is about making choices when you can't have everything.

Economics starts with one simple fact: people want more than they can have. You may want a new phone, a trip, and money in savings. But your paycheck covers only some of these. This lesson teaches the core ideas that grow from that fact:

  • scarcity and opportunity cost,
  • incentives,
  • supply and demand and equilibrium,
  • price ceilings and floors,
  • specialization and comparative advantage, and
  • the difference between market and command economies.

How the GED tests this: These ideas are the backbone of the economics questions. Expect to:

  • read a supply-and-demand graph and find equilibrium, a shortage, or a surplus;
  • predict what happens when demand or supply shifts;
  • find the opportunity cost in a short story about a person, business, or government;
  • spot incentives in a policy description;
  • use a small production table to decide which country has a comparative advantage;
  • sort features of economic systems.

Most items give you all the data you need. Your job is to use the definitions carefully. If you know the vocabulary well, you are halfway there.

Words to know

Key terms

  • scarcity — limited resources compared to unlimited wants (a city with $2 million but $4 million in needs).
  • opportunity cost — the value of the next-best alternative given up (studying instead of working a $60 shift).
  • trade-off — giving up some of one thing to get more of another.
  • incentive — a reward (positive) or penalty (negative) that encourages a change in behavior (a rebate; a fine).
  • demand — how much buyers are willing and able to buy at each price.
  • law of demand — as price rises, quantity demanded falls (and vice versa).
  • supply — how much sellers are willing and able to sell at each price.
  • law of supply — as price rises, quantity supplied rises.
  • equilibrium — the price and quantity where quantity demanded = quantity supplied.
  • shortage — quantity demanded > quantity supplied (price is too low).
  • surplus — quantity supplied > quantity demanded (price is too high).
  • price ceiling — a legal maximum price (rent control).
  • price floor — a legal minimum price (minimum wage).
  • specialization — focusing on producing a few goods or tasks (a bakery that only makes bread).
  • absolute advantage — being able to produce more of a good with the same resources.
  • comparative advantage — producing a good at a lower opportunity cost than someone else.
  • market economy — individuals and businesses make economic decisions; prices guide them.
  • command economy — the government decides what, how, and for whom to produce.
  • mixed economy — a blend of market and government decisions (the United States).

All Social Studies words in the glossary

Scarcity, opportunity cost, and incentives

In plain words: You can't have everything, so every choice means giving something up.

Scarcity means there is not enough to go around. It affects everyone — people, businesses, and governments. Money, time, workers, and land are all limited. So every choice involves a trade-off: you get more of one thing by giving up some of another.

Opportunity cost is the one next-best option you give up. It is not the price tag. It is also not every option you skipped.

Example: You have one free Saturday. You could work an extra shift, go to a ball game, or sleep in. You pick the shift. If the game was your second choice, the game is your opportunity cost.

Example: A city can spend $1 million on a new fire truck or on road repairs. It buys the truck. The opportunity cost is the road repairs.

Example: Jordan spends two hours studying for the GED. He could have worked a shift that pays $40. The opportunity cost is the $40 shift (the next-best use of that time).

Incentives shape choices. An incentive is a reward or a penalty that pushes people to act a certain way. Think of a store's "buy one, get one free" sale. It nudges you to buy two. Economists assume people respond to costs and benefits.

TypeExampleExpected behavior
Positive (reward)$500 rebate for an efficient water heaterMore people buy efficient heaters
Negative (penalty)10-cent fee per plastic bagPeople bring reusable bags
PositiveHigher pay for night shiftsMore workers sign up for nights
NegativeTax on cigarettesFewer cigarettes sold

On the GED, an incentive question often describes a policy. Then it asks what the policy is meant to do, or whether it worked. Look in the text for evidence that behavior changed.

Supply, demand, and equilibrium

In plain words: Prices settle where the amount people want to buy matches the amount sellers want to sell.

Think about a farmers' market. When strawberries are cheap, shoppers buy lots of them. But farmers bring fewer, because they earn less. When strawberries cost more, shoppers buy fewer, and farmers bring more.

  • Demand slopes down: at lower prices, buyers want more.
  • Supply slopes up: at higher prices, sellers offer more.
  • Where the two curves cross is equilibrium. At that price, the amount buyers want equals the amount sellers offer.
PriceQuantity demandedQuantity suppliedResult
$3750450Shortage of 300 → price rises
$4600600Equilibrium
$5450750Surplus of 300 → price falls
Supply and demand graph for the strawberry market table. Demand slopes down and supply slopes up; they cross at equilibrium E: 4 dollars and 600. At 3 dollars buyers want 750 but sellers offer 450, a shortage of 300. At 5 dollars sellers offer 750 but buyers want 450, a surplus of 300. Equilibrium, shortage and surplus $0 $1 $2 $3 $4 $5 $6 $7 0 150 300 450 600 750 900 1050 Quantity Price D S Shortage of 300 Surplus of 300 E ($4, 600)

Markets move toward equilibrium on their own.

  • With a surplus (too much), sellers cut prices to sell the extra goods.
  • With a shortage (too little), buyers compete, and sellers raise prices.

Shifts. A change in price moves you along a curve. A change in anything else shifts the whole curve.

  • Demand shifts when something changes for buyers. Examples: income, tastes, the number of buyers, expectations, or the price of related goods. Related goods are substitutes (used instead of each other, like butter and margarine) and complements (used together, like hot dogs and buns).
  • Supply shifts when something changes for sellers. Examples: the cost of inputs, technology, the number of sellers, weather, or taxes.
ChangePriceQuantity
Demand increases (shift right)↑↑
Demand decreases (shift left)↓↓
Supply increases (shift right)↓↑
Supply decreases (shift left)↑↓

Example: A frost destroys orange trees. → The supply of oranges decreases. → Orange prices rise, and fewer oranges are sold.

Illustrative supply and demand graph for oranges after a frost. Supply S shifts left to S2. The equilibrium moves from E to E2: price rises from P1 to P2 and quantity falls from Q1 to Q2. A frost decreases the supply of oranges Quantity Price D S S2 E E2 Q2 Q1 P2 P1 Supply shifts left: price up, quantity down Illustrative graph (no real data)

An increase in demand

Supply and demand graph showing an increase in demand. Original demand D crosses supply S at E: 4 dollars and 600 pints. New demand D2, a dashed line to the right of D, crosses S at E2: 5 dollars and 750 pints. An increase in demand raises both the equilibrium price and quantity. An Increase in Demand $0 $1 $2 $3 $4 $5 $6 $7 $8 0 150 300 450 600 750 900 1,050 1,200 Quantity (pints per day) Price per pint D S D2 E2 E

Demand shifts from D to D2. The new equilibrium E2 is at a higher price ($5) and a higher quantity (750) than the original E ($4, 600).

Price ceilings and price floors

In plain words: If the law holds a price too low, there is not enough to go around. If the law holds a price too high, extra goods are left over.

Sometimes governments set prices by law.

  • A price ceiling is a legal maximum — the highest price allowed. It matters only if it is set below equilibrium. Result: a shortage. Example: Rent control can leave more renters looking than apartments available. Example: Gas price caps in the 1970s led to long lines at gas stations.
  • A price floor is a legal minimum — the lowest price allowed. It matters only if it is set above equilibrium. Result: a surplus. Example: Farm price supports can leave extra crops unsold. Example: Many economists view the minimum wage as a price floor in the labor market. If it is set above the equilibrium wage, more people may want jobs than employers want to fill.
Two illustrative supply and demand graphs. Left: a price ceiling set below the equilibrium price of 4 dollars, at 3 dollars, creates a shortage because quantity demanded is greater than quantity supplied. Right: a price floor set above equilibrium, at 5 dollars, creates a surplus because quantity supplied is greater than quantity demanded. Price ceiling vs. price floor $0 $1 $2 $3 $4 $5 $6 $7 Quantity Price D S E shortage Ceiling $3 (below equilibrium) $0 $1 $2 $3 $4 $5 $6 $7 Quantity D S E surplus Floor $5 (above equilibrium) Illustrative graph using the strawberry market above

Memory trick: A ceiling is up high. But it only "bites" when it's pushed down below equilibrium. A floor is low. But it only bites when it's raised up above equilibrium.

To find the size of the shortage or surplus, use the legal price. Find the difference between quantity demanded and quantity supplied at that price.

Specialization, comparative advantage, and economic systems

In plain words: Do the job where you give up the least, and trade for everything else.

Specialization means focusing on what you do best and trading for the rest. It raises total output. Think of a restaurant kitchen. One cook grills, and another makes salads. Each gets faster at one job. In the same way, a worker who only bakes bread gets faster at it. A country that focuses on what it makes cheaply can trade for other goods.

Comparative advantage tells you what to specialize in. Compare opportunity costs, not total output.

CountryWheat per workerCloth per workerCost of 1 clothCost of 1 wheat
Northland632 wheat0.5 cloth
Southland221 wheat1 cloth

Northland has the absolute advantage in both goods — it makes more of each. But Southland gives up less to make cloth. So Southland has the comparative advantage in cloth. Northland has it in wheat. Both countries gain if each specializes. They then trade at a price between their two opportunity costs.

Economic systems answer three questions:

  1. What should be produced?
  2. How should it be produced?
  3. For whom is it produced?
SystemWho decides?Example
TraditionalCustom and traditionSmall subsistence farming communities
CommandCentral government plannersFormer Soviet Union, North Korea
MarketIndividuals and businesses via pricesNo pure example exists; it is a model
MixedMostly markets, with government rolesUnited States, Canada, most countries today
Formula

Quick calculations

\text{shortage} = Q_{\text{demanded}} - Q_{\text{supplied}} \quad (\text{price below equilibrium}) \text{surplus} = Q_{\text{supplied}} - Q_{\text{demanded}} \quad (\text{price above equilibrium}) \text{opportunity cost of 1 unit of X} = \dfrac{\text{units of Y given up}}{\text{units of X gained}}

Example: a worker makes 6 wheat or 3 cloth. Cost of 1 cloth = \dfrac{6}{3} = 2 wheat.

Worked example

Example 1: Finding a shortage

Source: At $10, buyers want 500 concert T-shirts; sellers offer 200. At $20, buyers want 300; sellers offer 300. At $30, buyers want 100; sellers offer 400.

Question: If the price is fixed at $10, what happens?

Think-aloud:

  1. Equilibrium is $20 (300 = 300). $10 is below equilibrium.
  2. At $10: demanded 500, supplied 200. Demand > supply → shortage.
  3. Size: 500 - 200 = 300 shirts.
  4. Eliminate "surplus of 300" (direction reversed) and "shortage of 500" (that's total demand, not the gap).
Supply and demand graph for concert T-shirts. Demand passes through 500 shirts at 10 dollars, 300 at 20 dollars and 100 at 30 dollars. Supply passes through 200 at 10 dollars, 300 at 20 dollars and 400 at 30 dollars. Equilibrium is 20 dollars and 300 shirts. A price fixed at 10 dollars gives quantity supplied 200 and quantity demanded 500, a shortage of 300 shirts. Concert T-shirts: price fixed at $10 $0 $5 $10 $15 $20 $25 $30 $35 0 100 200 300 400 500 600 Quantity of T-shirts Price D S Shortage = 500 − 200 = 300 200 500 E ($20, 300) fixed price $10

Answer: a shortage of 300 T-shirts.

Worked example

Example 2: Predicting a shift

Source: "A new machine cuts the cost of making solar panels in half."

Question: What happens to the price and quantity of solar panels?

Think-aloud:

  1. Lower production cost affects sellers, so the supply curve shifts.
  2. Cheaper to make → sellers offer more at every price → supply shifts right (increases).
  3. Supply increases → price falls, quantity rises.
  4. Trap: "demand increases because panels are cheaper." A lower price causes a movement along the demand curve, not a shift of demand.
Illustrative supply and demand graph for solar panels. A cheaper machine shifts supply S right to S2. The equilibrium moves from E to E2: price falls from P1 to P2 and quantity rises from Q1 to Q2. The demand curve does not move. Cheaper production increases the supply of solar panels Quantity Price D S S2 E E2 Q2 Q1 P2 P1 Supply shifts right: price down, quantity up Illustrative graph (no real data)

Answer: price decreases and quantity sold increases.

Worked example

Example 3: Opportunity cost in a government decision

Source: "The county had enough money for one project: a new bridge or a new clinic. Commissioners chose the bridge, saying traffic was the bigger problem."

Question: What is the opportunity cost of the county's decision?

Think-aloud:

  1. Scarcity: money for only one project.
  2. Choice made: the bridge.
  3. Next-best alternative given up: the clinic.
  4. Eliminate "the cost of the bridge" (a money price, not an alternative) and "less traffic" (a benefit of the bridge).
Decision diagram for the county budget. Scarcity: money for only one project. Choice made: the new bridge. Next-best alternative given up: the new clinic, which is the opportunity cost. Opportunity cost = the next-best option given up Money for ONE project Chosen: new bridge Given up: new clinic = opportunity cost

Answer: the new clinic.

Worked example

Example 4: Comparative advantage between two workers

Source: In one hour, Ana can paint 4 chairs or build 2 tables. Ben can paint 3 chairs or build 1 table.

Question: Who should build tables?

Think-aloud:

  1. Ana's cost of 1 table: 4 \div 2 = 2 chairs. Ben's cost of 1 table: 3 \div 1 = 3 chairs.
  2. Ana gives up fewer chairs per table → Ana has the comparative advantage in tables.
  3. Ben's cost of 1 chair: 1 \div 3 \approx 0.33 table. Ana's: 2 \div 4 = 0.5 table. Ben has the comparative advantage in chairs.
  4. Trap: "Ana should do both because she is faster at both." That is absolute advantage; total output is higher when each specializes.
Graph of one hour of production for two workers. Ana can paint 4 chairs or build 2 tables; her line runs from 4 chairs to 2 tables. Ben can paint 3 chairs or build 1 table; his line runs from 3 chairs to 1 table. Each table costs Ana 2 chairs but costs Ben 3 chairs, so Ana has the comparative advantage in tables and Ben in chairs. One hour of work: Ana vs. Ben 0 1 2 3 4 5 0 1 2 Tables built Chairs painted Ana Ben Cost of 1 table Ana: 4 ÷ 2 = 2 chairs Ben: 3 ÷ 1 = 3 chairs Ana gives up less → Ana builds tables; Ben paints chairs

Answer: Ana should build tables; Ben should paint chairs.

Common mistake

Common traps

  • Shortage vs. surplus. Wrong: "A ceiling causes a surplus." Right: a ceiling below equilibrium causes a shortage; a floor above equilibrium causes a surplus.
  • Opportunity cost = price. Wrong: "The opportunity cost of the $2 million park is $2 million." Right: it is the next-best project the money could have paid for.
  • Counting every alternative. Wrong: adding up all options you skipped. Right: only the single next-best one.
  • Absolute vs. comparative advantage. Wrong: "The country that makes more cloth has the comparative advantage in cloth." Right: the country that gives up less to make cloth has it.
  • Shift vs. movement along a curve. Wrong: "Price fell, so demand increased." Right: a price change moves along the demand curve (quantity demanded changes); only non-price factors shift the curve.
  • Reading the wrong axis. Wrong: calling 600 pints the equilibrium "price." Right: price is on the vertical axis, quantity on the horizontal.
Test strategy

GED strategy for economic concepts

  • Label the graph first: which line is supply (up) and which is demand (down)? What are the units on each axis?
  • Find equilibrium before anything else. Then decide if a given price is above (surplus) or below (shortage).
  • For shifts, ask "buyers or sellers?" Income, tastes, and population affect demand; costs, technology, and weather affect supply.
  • Use the table if one is given—it is more exact than reading the graph.
  • For opportunity cost, ask "What would they have done instead?"
  • For comparative advantage, compute both opportunity costs and choose the lower one. Ignore who makes more.
  • Watch for definitions in the stem. If the question defines a term, use its definition even if you learned it slightly differently.

Check yourself

Fundamental economic concepts
The Market for Strawberries

Farmers at a busy farmers' market sell fresh strawberries by the pint. The graph shows the demand (D) for strawberries and the supply (S) of strawberries at different prices.

Supply and demand graph for strawberries. Price per pint on the vertical axis from 0 dollars to 8 dollars; quantity in pints per day on the horizontal axis from 0 to 1,200 in steps of 150. Demand line D falls from 8 dollars at 0 pints to 0 dollars at 1,200 pints. Supply line S rises from 0 dollars at 0 pints to 8 dollars at 1,200 pints. They cross at point E: price 4, dollars quantity 600. At 2 dollars: demand 900, supply 300. At 3 dollars: demand 750, supply 450. At 5 dollars: demand 450, supply 750. At 6 dollars: demand 300, supply 900. Market for Strawberries $0 $1 $2 $3 $4 $5 $6 $7 $8 0 150 300 450 600 750 900 1,050 1,200 Quantity (pints per day) Price per pint D S E
Price per pintQuantity demandedQuantity supplied
$2900300
$3750450
$4600600
$5450750
$6300900

Based on the graph and table, what is the equilibrium price of a pint of strawberries?

Answer choices
Hint

Equilibrium is where the two lines cross—where quantity demanded equals quantity supplied.

Check yourself

Fundamental economic concepts
The Market for Strawberries

Farmers at a busy farmers' market sell fresh strawberries by the pint. The graph shows the demand (D) for strawberries and the supply (S) of strawberries at different prices.

Supply and demand graph for strawberries. Price per pint on the vertical axis from 0 dollars to 8 dollars; quantity in pints per day on the horizontal axis from 0 to 1,200 in steps of 150. Demand line D falls from 8 dollars at 0 pints to 0 dollars at 1,200 pints. Supply line S rises from 0 dollars at 0 pints to 8 dollars at 1,200 pints. They cross at point E: price 4, dollars quantity 600. At 2 dollars: demand 900, supply 300. At 3 dollars: demand 750, supply 450. At 5 dollars: demand 450, supply 750. At 6 dollars: demand 300, supply 900. Market for Strawberries $0 $1 $2 $3 $4 $5 $6 $7 $8 0 150 300 450 600 750 900 1,050 1,200 Quantity (pints per day) Price per pint D S E
Price per pintQuantity demandedQuantity supplied
$2900300
$3750450
$4600600
$5450750
$6300900

Suppose farmers charge $5 per pint. Based on the table, what will happen in this market?

Answer choices
Hint

At $5, compare how many pints buyers want with how many pints sellers bring.

Summary

  • Scarcity forces choices; the opportunity cost of a choice is the single next-best alternative given up.
  • Incentives—rewards and penalties—change behavior.
  • Demand slopes down, supply slopes up, and equilibrium is where they cross. Above it: surplus. Below it: shortage.
  • A price ceiling below equilibrium causes a shortage; a price floor above equilibrium causes a surplus.
  • Comparative advantage (lower opportunity cost), not absolute advantage, determines who should specialize in what.
  • Economies range from command (government decides) to market (prices decide); the U.S. is a mixed economy.
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