IAI Actuarial Core Principles · Business Economics
How Competitive Markets Operate: Demand, Supply and Equilibrium
A competitive market is one where many buyers and sellers take the price as given. Demand and supply set an equilibrium price and quantity. To solve questions, find where quantity demanded equals quantity supplied, then test shifts, elasticity, government intervention and surplus. Always draw the diagram and state the direction of change.
What this chapter covers
This chapter explains how prices and quantities are set in a competitive market. You start with demand, then supply, then bring them together to find equilibrium. After that you ask how sensitive buyers and sellers are to price changes (elasticity), what happens when the government steps in with price limits, taxes or subsidies, and how to judge whether the outcome is efficient using consumer and producer surplus.
The chapter is the base of the microeconomics part of CB2 Business Economics. Microeconomics carries a large share of the 2026 syllabus weighting (40%). Later topics such as market failure, firm behaviour, and imperfect competition all start from the demand and supply model. If you are weak here, those later chapters will feel harder than they are.
The chapter also links to macroeconomics. Ideas such as aggregate demand, aggregate supply and the effect of policy use the same logic of shifts, equilibrium and adjustment. For an actuarial student, it also helps you read how insurance, pensions and investment markets respond to price changes and regulation.
CB2 opens with multiple-choice questions of 2 marks each and then moves to written questions, and this chapter suits both. MCQs often test a single shift, a direction of change or a simple elasticity calculation, which you can win quickly if the basics are firm. Written questions ask you to explain with diagrams and apply the model to a real-world scenario, such as a tax, a price cap or a change in input costs. Marks go to clear reasoning, correct diagrams and stated assumptions. Since CB1, CB2 and CB3 need at least 50% to pass (as confirmed by IAI session by session), solid, repeatable marks from this chapter help a lot.
How competitive markets operate: topics in the order to study them
- 1Demand and Law of DemandStart here because it is one half of the model and introduces movements along a curve versus shifts of the curve.
- 2Supply and Law of SupplyStudy it next so you can handle the other half of the model with the same movement versus shift logic.
- 3Market Equilibrium and Price DeterminationThis joins demand and supply and is the tool you will use in every later topic.
- 4Price Elasticity of Demand and SupplyOnce you can find equilibrium, you measure how strongly quantity responds to price, which is needed for taxes and revenue questions.
- 5Government Intervention: Price Controls, Taxes and SubsidiesIt applies equilibrium and elasticity to policy, so it comes after both.
- 6Consumer and Producer Surplus and Market EfficiencyLast, because surplus lets you measure the gains and losses from equilibrium and from the interventions you just studied.
How to prepare How competitive markets operate
This chapter rewards a diagram-first habit. Build the model in small steps and practise each step until it is automatic.
- Learn the definitions in your own words: quantity demanded, demand, quantity supplied, supply, equilibrium, elasticity, surplus. Be able to say the difference between a movement along a curve and a shift of the curve.
- Draw demand and supply diagrams by hand, with labelled axes (price on the vertical axis, quantity on the horizontal axis). Practise shifting each curve for each cause and write the new equilibrium price and quantity.
- Practise numerical work with linear demand and supply equations. Set quantity demanded equal to quantity supplied, solve for price, then for quantity. Check by substituting back into both equations.
- Learn the elasticity formulas: price elasticity of demand = % change in quantity demanded ÷ % change in price. Practise reading the result: above 1 is elastic, below 1 is inelastic, equal to 1 is unit elastic (using the size, ignoring the sign).
- For each intervention (price ceiling, price floor, tax, subsidy), draw the before and after diagrams and write down who gains, who loses and what happens to quantity traded. Link the tax burden split to relative elasticity.
- Calculate surplus as areas of triangles and rectangles on your diagrams, and explain deadweight loss in one or two sentences.
- Finish with timed practice: a set of MCQs in 2 minutes each at most, then one written question with a diagram and a short explanation. Review every error and record the cause.
Common mistakes in How competitive markets operate
Confusing a movement along a curve with a shift of the curve.
Fix: Ask first: is the cause the good's own price? If yes, move along the curve. If it is anything else, shift the curve.
Drawing diagrams without labels or with the wrong axis.
Fix: Label both axes, both curves, the old and new equilibrium (E1, E2), and the prices and quantities. Examiners give marks for clear labelling.
Applying a price ceiling or floor that is not binding.
Fix: Compare the control with the equilibrium price first. A ceiling above equilibrium or a floor below equilibrium has no effect.
Mixing up elasticity with slope.
Fix: Use the percentage change formula every time. Remember that elasticity changes along a straight-line demand curve even though slope does not.
Thinking the party that pays the tax to the government bears the tax.
Fix: Split the burden by comparing the new price paid by buyers and received by sellers with the old equilibrium price. The less elastic side bears more.
Stating a result without explaining the reasoning in written answers.
Fix: Write a chain: cause, curve shifted, direction, new equilibrium, effect on price and quantity. Add one sentence on who gains or loses.
Last-day revision: How competitive markets operate
- Law of demand: other things equal, a higher price lowers quantity demanded.
- Law of supply: other things equal, a higher price raises quantity supplied.
- A price change moves you along a curve; a change in any other factor shifts the curve.
- Equilibrium is where quantity demanded equals quantity supplied, so there is no shortage or surplus.
- Price above equilibrium creates excess supply; price below equilibrium creates excess demand.
- Price elasticity of demand = % change in quantity demanded ÷ % change in price.
- The more inelastic side of the market bears more of a tax.
- A binding price ceiling is set below equilibrium and causes a shortage; a binding price floor is set above equilibrium and causes a surplus.
- A subsidy shifts the supply curve right and lowers the price paid by buyers.
- Consumer surplus is the gap between willingness to pay and price; producer surplus is the gap between price and the minimum acceptable price.
- A competitive equilibrium maximises total surplus, and a tax or binding control creates deadweight loss.
How competitive markets operate practice questions
- When the price of a product rises from ₹80 to ₹88 per unit, a firm's quantity supplied rises from 500 to 540 units. Using the percentage cha…
- In a perfectly competitive market with a downward-sloping demand curve and an upward-sloping supply curve, consumer surplus at the equilibri…
- In a competitive market, consumer surplus for a unit of a good is best defined as:
- A pharmacy chain in Pune observes that when the price of a branded vitamin tablet strip falls from Rs 100 to Rs 90, the quantity sold rises …
- Linear demand for a mutual fund's online investing app subscriptions is Qd = 12,000 - 40P, where P is the monthly fee in rupees. At a fee of…
- The market for a commodity has demand Qd = 500 - 4P and supply Qs = 100 + 6P, where P is in rupees. What is the equilibrium price and quanti…
- In a competitive market for term-insurance policies, a rise in household incomes increases demand at every price, while supply is unchanged.…
- The market demand for a policy-comparison service is P = 100 - Q and supply is P = 20 + Q, with P in rupees and Q in thousands of users. Wha…
How competitive markets operate in other exams
The same ground in other exams, if you are preparing for more than one or want another angle on it.
How competitive markets operate: frequently asked questions
Is this chapter more theory or more calculation?
It is mostly theory and diagrams, with some simple calculations. Expect to solve linear demand and supply equations, work out elasticity and compute surplus from areas. Practise both so that you can answer MCQs fast and write clear explanations.
How long should I spend on this chapter?
It is a foundation chapter, so give it enough time to be fluent, because later microeconomics topics depend on it. If you study alongside work, split it into short sessions: one topic each, then a combined practice session at the end.
Do I need to memorise the elasticity formulas?
Yes. Learn the percentage change formula and the meaning of elastic, inelastic and unit elastic. Then practise a few numbers so you can compute and interpret the result quickly under time pressure.
How do I prepare for the written questions on this chapter?
Practise past-style questions with a diagram and a short explanation. State your assumptions, such as other things equal and a competitive market. Show the before and after equilibrium and say clearly what happens to price, quantity and surplus.