WAEC Economics Graphs and Diagrams: A Visual Guide to Demand, Supply, Cost and Revenue Curves

Economics graphs and diagrams are important tools for explaining how consumers, producers and markets behave. They help students present relationships between economic variables clearly, interpret changes in market conditions and explain concepts that may be difficult to describe using words alone.

For WAEC WASSCE Economics candidates, understanding these diagrams is an important part of examination preparation. You may be asked to draw a demand curve, illustrate an increase in supply, determine equilibrium price and quantity, or use cost and revenue curves to explain a firm's behaviour. In some questions, you may also need to interpret an existing diagram and explain what it represents.

However, knowing the shape of a curve is not enough. You must understand what the axes represent, how to label the curves, why they move or shift, and how to explain the economic meaning of a change.

WAEC's published examiner reports have repeatedly identified weaknesses in graphical analysis and graph interpretation among Economics candidates. Its reports also emphasise the need to use correct economic terminology and explain points adequately rather than merely identifying them. 

This guide explains the major Economics graphs and diagrams students should understand, how to construct and interpret them, and how to avoid common mistakes when answering WAEC questions.

Table of Content

Why Are Graphs and Diagrams Important in WAEC WASSCE Economics?

How Do You Draw and Label an Economics Graph Correctly?

What Is a Demand Curve, and How Do You Draw It?

What Is a Supply Curve, and How Do You Interpret It?

How Do Demand and Supply Determine Equilibrium Price and Quantity?

What Happens When Demand Increases?

What Happens When Supply Increases?

How Do You Draw and Interpret Cost Curves?

What Are Total Revenue, Average Revenue and Marginal Revenue Curves?

How Can You Practise WAEC Economics Graphs Effectively?

Frequently Asked Questions About WAEC Economics Graphs and Diagrams

Conclusion

Why Are Graphs and Diagrams Important in WAEC WASSCE Economics?

Graphs make it easier to show relationships between economic variables. Instead of describing every change in a long paragraph, you can use a correctly drawn diagram to illustrate what happens and then explain the result in words.

For example, a demand and supply diagram can show how an increase in demand affects equilibrium price and quantity. A cost curve can illustrate how a firm's average cost changes as output increases, while a revenue curve can show the relationship between sales and the money a firm earns.

The WAEC Economics syllabus includes basic tools of economic analysis, demand, supply, price determination, production, cost and revenue, and market structures. These areas provide the foundation for understanding the diagrams discussed in this article.

Candidates should therefore practise both drawing diagrams and answering questions based on them. If you need additional practice with Economics concepts, explore ExamGuide's WAEC and SSCE learning resources to support your revision with examination practice.

How Do You Draw and Label an Economics Graph Correctly?

Before learning individual diagrams, understand the basic rules that apply to most Economics graphs.

1. Draw and label the axes correctly

Most introductory Economics diagrams use two axes. The vertical axis is called the Y axis, while the horizontal axis is called the X axis.

For a standard demand and supply diagram, price is usually placed on the vertical axis and quantity on the horizontal axis. For cost and revenue diagrams, cost or revenue is generally placed on the vertical axis, while output is placed on the horizontal axis.

Always read the question carefully because the variables required may differ depending on the diagram.

2. Label every curve

Use appropriate labels such as D for demand, S for supply, MC for marginal cost, AC for average cost, TR for total revenue and MR for marginal revenue.

If a curve shifts, distinguish the original curve from the new one. For example, D1 and D2 can represent the original and new demand curves.

3. Mark important points clearly

Where a question requires equilibrium, indicate the intersection of demand and supply curves. Use dotted lines to project the equilibrium point to the axes if you need to identify the corresponding price and quantity.

For cost and revenue diagrams, identify the points or output levels requested in the question, such as the profit maximising output where marginal revenue equals marginal cost.

4. Explain the diagram after drawing it

A diagram should support your answer, not replace the explanation. State what the curves represent, identify the change being illustrated and explain its effect.

For example, if an increase in demand shifts the demand curve to the right while supply remains unchanged, the equilibrium price and quantity will generally rise.

This combination of correct drawing, labelling and explanation helps you communicate your understanding clearly.

What Is a Demand Curve, and How Do You Draw It?

A demand curve shows the relationship between the price of a commodity and the quantity demanded over a given period, assuming other relevant factors remain constant.

The law of demand states that, other things being equal, quantity demanded generally increases when price falls and decreases when price rises.

To draw a demand curve, place price on the vertical axis and quantity demanded on the horizontal axis. Plot the quantities demanded at different prices and connect the points with a downward sloping line or curve.

For example, suppose consumers demand 10 bags of rice when the price is ₦80,000 per bag and 20 bags when the price falls to ₦60,000, assuming the figures refer to the same market and period. Plot each price against its corresponding quantity and connect the points.

The resulting demand curve slopes downwards from left to right.

What Causes Movement Along a Demand Curve?

A movement along a demand curve occurs when the price of the commodity itself changes, assuming other factors remain constant.

When price falls, quantity demanded increases. This is called an extension of demand. When price rises, quantity demanded decreases, producing a contraction of demand.

The important point is that the original demand curve does not shift. The consumer moves from one point to another along the same curve because the commodity's own price has changed.

What Causes a Shift in the Demand Curve?

A shift occurs when a factor other than the commodity's own price changes demand.

Factors that may shift demand include consumer income, tastes and preferences, population, expectations about future prices, and the prices of related goods.

For example, if consumer income rises and rice is treated as a normal good, demand for rice may increase at every price. The demand curve shifts to the right.

If demand decreases, the curve shifts to the left. This means consumers are willing and able to buy less at each price than before.

Remember that a price change causes movement along the curve, while a change in another determinant of demand can shift the curve.

What Is a Supply Curve, and How Do You Interpret It?

A supply curve shows the relationship between the price of a commodity and the quantity producers are willing and able to offer for sale over a given period.

The law of supply states that, other things being equal, quantity supplied generally increases as price rises and decreases as price falls.

To draw a supply curve, put price on the vertical axis and quantity supplied on the horizontal axis. Plot the quantities supplied at different prices and connect the points. A typical supply curve slopes upwards from left to right.

For example, a farmer may be willing to supply 50 baskets of tomatoes when the market price is ₦10,000 per basket but 100 baskets when the price rises to ₦15,000, assuming other conditions remain unchanged.

The higher price may encourage the farmer to offer more tomatoes for sale because production and marketing become more rewarding.

What Is the Difference Between a Movement Along Supply and a Shift in Supply?

A movement along the supply curve occurs when the commodity's own price changes. A rise in price generally leads to an extension of supply, while a fall in price leads to a contraction of supply.

A shift in supply occurs when another factor changes the quantity producers are willing and able to supply at each price.

Important determinants of supply include production costs, technology, taxes, subsidies, weather conditions and the prices of other goods producers could make.

For example, if improved technology reduces the cost of producing bread, bakeries may be able to supply more bread at each price. The supply curve shifts to the right.

If the cost of flour or electricity rises substantially, production may become more expensive. Supply may decrease, shifting the curve to the left.

When answering a WAEC question, identify the factor that has changed before deciding whether the curve should move along its original position or shift.

How Do Demand and Supply Determine Equilibrium Price and Quantity?

Market equilibrium occurs when the quantity demanded equals the quantity supplied at a particular price.

To draw the diagram, place price on the vertical axis and quantity on the horizontal axis. Draw a downward sloping demand curve and an upward sloping supply curve. The point where the two curves intersect represents equilibrium.

Project the intersection to the vertical axis to identify the equilibrium price and to the horizontal axis to identify the equilibrium quantity.

At equilibrium, the quantity buyers want to purchase equals the quantity sellers want to sell. Assuming other conditions remain unchanged, there is no immediate pressure from excess demand or excess supply to change the market price.

What Happens When Demand Increases?

When demand increases and supply remains unchanged, the demand curve shifts to the right. The new intersection with the supply curve generally indicates a higher equilibrium price and a greater equilibrium quantity.

For example, if more consumers begin buying a particular brand of cooking oil, sellers may experience increased demand. If supply does not change immediately, the market price may rise, and more units may be sold.

What Happens When Supply Increases?

When supply increases and demand remains unchanged, the supply curve shifts to the right. The new equilibrium generally has a lower price and a greater quantity.

For instance, if a good harvest increases the supply of tomatoes, more tomatoes become available in the market. If demand remains unchanged, the equilibrium price may fall while the quantity exchanged increases.

For a decrease in supply, the curve shifts to the left. The equilibrium price generally rises, while equilibrium quantity falls, assuming demand remains unchanged.

These relationships are common foundations for data response and diagram questions. You can practise identifying shifts and interpreting their effects through ExamGuide's examination practice platform.

How Do You Draw and Interpret Cost Curves?

Cost curves show how a firm's production costs relate to its output. They are important when studying production decisions and market structures.

The horizontal axis represents output, while the vertical axis represents cost per period or unit, depending on the measure being illustrated.

Total Cost Curve

Total cost is the sum of total fixed cost and total variable cost.

Fixed costs do not change directly with output in the short run, while variable costs change as production changes. Total cost therefore includes both components.

A total cost curve generally begins at the level of fixed cost when output is zero and rises as output increases, assuming production involves variable costs.

When explaining a total cost diagram, identify the output level and the corresponding total cost. Avoid describing total cost as the cost per unit because that is average cost.

Average Cost Curve

Average cost is total cost divided by output.

It is often represented by a U shaped curve in introductory short run cost analysis. Initially, average cost may fall as output increases because fixed costs are spread over more units and production becomes more efficient. Beyond a certain point, average cost may rise as diminishing returns or capacity constraints increase the cost of additional production.

When drawing an average cost curve, label it AC or ATC, depending on the notation used in your class materials. Make sure you understand whether the question refers to average total cost or another average cost measure.

Marginal Cost Curve

Marginal cost is the additional cost of producing one more unit of output.

It is commonly represented by a U shaped curve in standard short run analysis. Marginal cost may initially fall as production becomes more efficient, then rise as diminishing marginal returns set in.

In the conventional cost diagram, the marginal cost curve intersects the average variable cost and average total cost curves at their respective minimum points.

This relationship is important because marginal cost helps explain how average costs change. When marginal cost is below average cost, it pulls the average down. When marginal cost is above average cost, it pulls the average up.

What Are Total Revenue, Average Revenue and Marginal Revenue Curves?

Revenue is the money a firm receives from selling its output. Three important measures are total revenue, average revenue and marginal revenue.

Total Revenue Curve

Total revenue is calculated by multiplying the price per unit by the quantity sold.

If a trader sells 20 bags of rice at ₦70,000 per bag, total revenue is ₦1,400,000.

Under a constant selling price, total revenue increases in direct proportion to the quantity sold, so the total revenue curve is a straight line from the origin. If price changes as output increases, the shape may differ.

Average Revenue Curve

Average revenue is total revenue divided by the quantity sold. In ordinary sales analysis, it is equal to the price received per unit.

For a firm in a perfectly competitive market, the individual firm's average revenue curve is horizontal at the market price because the firm can sell its output at that price under the model's assumptions.

For a firm facing a downward sloping demand curve, average revenue generally slopes downwards as the firm sells more output at lower prices.

Marginal Revenue Curve

Marginal revenue is the additional revenue earned from selling one more unit of output.

Under perfect competition, marginal revenue equals price and average revenue for the individual firm. Under a downward sloping demand curve, marginal revenue is generally below average revenue because selling additional units may require the firm to lower its price.

In standard diagrams for a firm facing a downward sloping linear demand curve, the marginal revenue curve lies below the average revenue curve.

When answering questions about revenue, be clear about the type of market being described. The relationship between average revenue and marginal revenue depends on the market conditions and assumptions.

How Do Cost and Revenue Curves Show Profit Maximisation?

Cost and revenue diagrams can be used to analyse a firm's output decision.

A standard rule for profit maximisation is that marginal revenue equals marginal cost, provided the relevant conditions for a maximum are satisfied. In a conventional diagram, the firm chooses the output where the marginal cost curve intersects the marginal revenue curve while marginal cost is rising through marginal revenue.

The intersection identifies the profit maximising output under the model. To determine whether the firm makes a profit, breaks even or incurs a loss, compare average revenue with average total cost at that output.

If average revenue exceeds average total cost, the firm earns an economic profit. If they are equal, the firm breaks even. If average revenue is below average total cost, the firm incurs a loss.

Do not confuse the point where marginal cost intersects average cost with the profit maximising output. WAEC's published 2023 Economics Paper 2 feedback specifically noted that some candidates identified the wrong equilibrium output and price by using the point where marginal cost equalled average total cost instead of the point where marginal cost equalled marginal revenue. 

What Common Mistakes Should You Avoid When Drawing Economics Diagrams?

Students can understand the theory but still lose marks when their diagrams do not communicate the intended relationship clearly.

Incorrectly labelled axes: Always check whether the question requires price, quantity, cost, revenue or output on each axis. Labelling the axes incorrectly can change the meaning of the entire diagram.

Confusing movement with a shift: A change in the commodity's own price usually produces movement along a demand or supply curve. Changes in other determinants may shift the curve. Identify the cause before drawing.

Leaving out curve labels: Label curves clearly as D, S, MC, AC, TR or MR, as appropriate. When showing a change, use distinct labels for the original and new curves.

Failing to mark equilibrium: If the question asks for equilibrium price and quantity, indicate the intersection and project the values to the axes where appropriate.

Drawing without explaining: A diagram alone may not answer a question asking you to explain a change. State the initial position, describe the shift or movement, and explain the resulting effect on price, quantity, cost, revenue or output.

Using the wrong terminology: Learn the difference between demand and quantity demanded, supply and quantity supplied, average cost and marginal cost, and average revenue and marginal revenue. These terms describe different economic concepts.

Making diagrams difficult to read: Use a ruler where appropriate, draw clear curves and avoid unnecessary shading or markings. Make sure each label is legible.

How Can You Practise WAEC Economics Graphs Effectively?

The best way to improve is to practise drawing diagrams from memory, interpreting existing diagrams and explaining changes in writing.

Start with one diagram at a time. Draw it, label the axes and curves, and explain what it shows. Then practise a question that changes one of the economic variables. For example, draw an equilibrium diagram and show what happens when demand increases while supply remains unchanged.

Next, practise interpreting diagrams you did not draw yourself. Identify the axes, curves, intersection points and direction of any shift. Explain what the diagram means before looking at the answer or explanation.

You can also keep a notebook containing your most important diagrams. For each one, write down its purpose, correct labels, typical shape and the relationships you must remember.

You can also use ExamGuide's SSCE practice resources alongside your class notes and past questions to reinforce your understanding of Economics concepts.

Parents can support students by helping them set aside regular practice time and encouraging them to explain each diagram aloud. Teachers and tutors can ask learners to draw the diagram first, then describe the economic change without relying on memorised paragraphs.

Frequently Asked Questions About WAEC Economics Graphs and Diagrams

1. Which Economics graphs should WAEC candidates know?

Candidates should understand demand and supply curves, market equilibrium diagrams, movements along and shifts of curves, and relevant cost and revenue curves. They should also study other diagrams required by their syllabus, including the production possibility curve and diagrams related to market structures.

2. How do you label a demand curve in WAEC Economics?

Place price on the vertical axis and quantity demanded on the horizontal axis. Label the curve D or DD. If the curve shifts, distinguish the original and new curves using labels such as D1 and D2.

3. What is the difference between an increase in demand and an increase in quantity demanded?

An increase in demand shifts the demand curve to the right because a factor other than the commodity's own price has changed. An increase in quantity demanded is an extension along the existing demand curve caused by a fall in the commodity's own price, assuming other factors remain constant.

4. What is the difference between an increase in supply and an increase in quantity supplied?

An increase in supply shifts the supply curve to the right because a determinant of supply has changed. An increase in quantity supplied is movement along the existing supply curve, usually caused by a rise in the commodity's own price.

5. How do you identify equilibrium price and quantity?

Find the intersection of the demand and supply curves. Project that point to the vertical axis to identify equilibrium price and to the horizontal axis to identify equilibrium quantity.

6. Why does a normal demand curve slope downwards?

A normal demand curve slopes downwards from left to right because, other things being equal, consumers generally demand more of a commodity at a lower price and less at a higher price.

7. Why does a supply curve usually slope upwards?

A typical supply curve slopes upwards because producers generally offer more units for sale at higher prices, assuming other factors remain unchanged. Higher prices may make additional production more worthwhile.

8. What is the difference between average cost and marginal cost?

Average cost is total cost divided by total output. Marginal cost is the additional cost of producing one more unit of output. They measure different aspects of production cost and should not be used interchangeably.

9. What is the difference between average revenue and marginal revenue?

Average revenue is total revenue divided by quantity sold, which is generally the price received per unit. Marginal revenue is the additional revenue earned from selling one more unit. Their relationship depends on the market structure and the firm's demand conditions.

10. How can I improve my performance in Economics diagram questions?

Practise drawing diagrams regularly without looking at your notes. Label every axis and curve, mark important points, interpret changes and explain the results in writing. Review past questions and examiner feedback to identify common errors and improve your answers.

Conclusion

WAEC Economics graphs and diagrams become easier to understand when you learn what each curve represents instead of memorising its shape alone. Demand and supply diagrams explain market behaviour, equilibrium diagrams show how price and quantity are determined, and cost and revenue curves help explain the decisions firms make about production and sales.

For every diagram you study, learn how to draw it, label it correctly, interpret changes and explain the economic relationship in clear sentences. Practise with past questions, review your mistakes and pay attention to the specific instructions in each question.

With consistent practice, you can develop the skills needed to present clearer diagrams and give more complete explanations in your WAEC Economics examination.