How prices, quantities, and competition actually work β so you can make better decisions on pricing, output, and where to play. One core idea runs through it all: people respond to incentives at the margin.
1The big idea
Thinking like an economist
Economics is really just the study of choice under scarcity. Three ideas unlock 80% of it:
Opportunity costThe true cost of anything = the next-best thing you gave up to get it. Not just the money β the foregone alternative.
Thinking at the marginDecisions are made in small steps: "should I do one more?" Compare the extra benefit vs the extra cost.
IncentivesPeople & firms respond predictably to rewards and penalties. Change the incentive β change the behaviour.
Memory hook π§ "There's no such thing as a free lunch." Every choice spends a resource you could've used elsewhere β that's opportunity cost in 6 words.
2The two curves
Demand & Supply
The whole engine of a market is two opposing forces. Demand = what buyers want at each price. Supply = what sellers will offer at each price.
Demand slopes down: cheaper β people buy more.
Supply slopes up: pricier β sellers offer more.
The law of demandAll else equal, when price rises, quantity demanded falls β and vice versa. Same logic in reverse for supply.
Memory hook π§ Demand goes Down. Supply goes up like a Staircase. The two letters tell you the slope.
3Where they meet
Market Equilibrium
Lay the two curves on the same graph. Where they cross is the equilibrium: the one price where the amount buyers want exactly equals the amount sellers offer. The market naturally settles here.
P* and Q* = the equilibrium price and quantity. Above P* β surplus (glut). Below P* β shortage.
Self-correctingPrice too high β unsold stock (surplus) β sellers cut prices β back toward P*. Price too low β empty shelves (shortage) β prices bid up β back toward P*.
4When the whole curve moves
Shifts vs. Movements
Critical distinction: a price change is a movement along a curve. But other factors move the entire curve left or right β changing the equilibrium.
A rightward shift (DββDβ) = buyers want more at every price.
Demand shiftersIncome, tastes/trends, price of related goods (substitutes & complements), expectations, number of buyers.
Supply shiftersInput costs, technology, taxes/subsidies, number of sellers, expectations.
Memory hook π§ Price changes = slide along the curve. Anything else = shift the whole curve. If it's not the good's own price, it's a shift.
5How sensitive?
Price Elasticity of Demand
Elasticity measures how much quantity responds to a price change. This is the single most useful pricing number a manager can know.
The core formula
PED =
% change in Quantity demanded% change in Price
Usually negative (price up β quantity down), so we read the absolute value. |PED| > 1 = elastic Β· |PED| < 1 = inelastic.
Elastic (>1): luxuries, many substitutes.
Inelastic (<1): necessities, few substitutes.
Elastic |PED|>1Demand very responsive. To raise revenue β cut price (sell many more). E.g. soft drinks, branded clothes.
Inelastic |PED|<1Demand barely responds. To raise revenue β raise price. E.g. petrol, insulin, cigarettes.
Two cousinsIncome elasticity = %ΞQ Γ· %Ξincome (normal vs inferior goods). Cross elasticity = %ΞQ of A Γ· %ΞPrice of B (positive = substitutes, negative = complements).
Memory hook π§ "Elastic stretches easily" β like a rubber band, quantity stretches a lot when price nudges. Inelastic = rigid, barely moves.
6One more unit?
Marginal Analysis
"Marginal" just means the next one. Every "should I produce/buy/hire more?" decision compares two marginals:
Marginal cost & revenue
MC =
Ξ Total CostΞ Quantity
MR =
Ξ Total RevenueΞ Quantity
MC = the cost of making one more unit Β· MR = the revenue from selling one more unit.
The golden ruleKeep producing as long as MR > MC (each extra unit adds profit). Stop where MR = MC. Past that, extra units cost more than they earn.
7The most important graph
Profit Maximization: MR = MC
This single rule sets the optimal output for any firm. Profit is maximised at the quantity where the marginal cost curve crosses the marginal revenue curve.
Produce up to Q* (where MR meets MC). One more unit beyond = losing money on each.
Memory hook π§ "Make money 'til the marginals match." Left of the cross, MR>MC = keep going. Right of it, MC>MR = pull back.
8Who you compete with
The Four Market Structures
How much pricing power you have depends on the competitive landscape. It's a spectrum β from zero power (perfect competition) to total control (monopoly).
Memory hook π§ Pricing power grows left β right: from price taker (perfect competition, you just accept the market price) to price maker (monopoly, you set it).
9Strategic interaction
Game Theory: The Prisoner's Dilemma
In an oligopoly, your best move depends on rivals' moves. Game theory maps this with a payoff matrix. The classic case shows why competitors often end up in a price war neither wants.
Each firm fears the other will cut β both cut β both land in the bottom-right (0/0), worse than cooperating (+10/+10).
Nash equilibriumA stable outcome where no player can do better by changing alone, given what the others do. Here it's "both cut price" β even though both would prefer to cooperate.
Why it mattersThis explains real price wars, ad spending arms-races, and why cartels are unstable: each member is always tempted to defect for short-term gain.
10Putting it to work
Pricing Strategies
Economics turns into a manager's most direct lever: price. Common approaches:
Cost-plusAdd a fixed markup to unit cost. Simple but ignores demand & competition.
Value-basedPrice on the value perceived by the customer, not your cost. Captures more margin.
Price discriminationCharge different prices to different segments (student/airline/peak pricing) to capture more total value.
PenetrationLow launch price to grab share fast, then raise. Works when demand is elastic.
SkimmingHigh launch price for eager early buyers, then lower over time. Works when demand is inelastic at the top.
Tie it together π§ Your elasticity (Β§5) tells you which way to move price; your market structure (Β§8) tells you how much freedom you have to move it at all.
π― Active recall
Cover the answer, say it out loud, then tap to check. Revisit today, in 3 days, and in a week. Bonus: re-draw the supply/demand and MR=MC graphs from memory.
What is opportunity cost β in one line?
The value of the next-best alternative you gave up when making a choice. (Not just the cash spent.)
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Why does the demand curve slope down but supply slope up?
Demand: lower price β buyers want more. Supply: higher price β sellers willing to produce more. (Hook: D goes Down, S like a Staircase.)
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Difference between a movement along vs a shift of a curve?
A change in the good's own price = movement ALONG the curve. Any other factor (income, tastes, input costsβ¦) = shifts the WHOLE curve left/right.
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Write the price-elasticity-of-demand formula.
PED = (% change in quantity demanded) Γ· (% change in price). |PED|>1 = elastic, |PED|<1 = inelastic.
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Your product is inelastic. Should you raise or cut price to grow revenue?
Raise it. Quantity barely falls, so higher price β higher total revenue. (Cut price only when demand is elastic.)
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State the profit-maximization rule.
Produce the quantity where Marginal Revenue = Marginal Cost (MR = MC). Keep going while MR>MC; stop when they're equal.
An outcome where no player can improve by changing their own move alone, given what everyone else does. In the prisoner's dilemma it's "both defect" β stable but not the best joint result.
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Module 2 of your MBA Β· Re-draw every graph from memory before moving on. π