These are original Marlbridge practice questions, not past exam questions. All questions use Valdoria, a fictional country whose currency is the valda (VD); all prices and quantities are fictional. The rubrics are a suggested Marlbridge rubric to help you check your work; they are not an official scoring guideline. Assumptions: in each question only the stated change happens and everything else stays the same; a four-function calculator is enough. When a question asks for a graph, draw it on paper and compare it with the description in the answer.
Question 1 (multiple choice · foundation)
Which event causes a movement along the demand curve for bus rides in Valdoria, rather than a shift of it?
- (A) The price of a bus ride rises from VD 1.50 to VD 1.80.
- (B) Valdorian household incomes fall.
- (C) The price of petrol for private cars rises.
- (D) A new university opens on a bus route and thousands of students arrive.
Answer and explanation
Answer: (A). A change in the good’s own price changes the quantity demanded. Buyers move along the existing curve; here the quantity demanded of bus rides falls.
- (B) Income is a determinant of demand, so it shifts the curve (left if bus rides are a normal good, right if they are inferior).
- (C) Car travel is a substitute for bus travel. Dearer petrol makes driving more expensive, so demand for bus rides increases: a shift right.
- (D) More buyers is a determinant. It increases demand: a shift right.
Question 2 (multiple choice · core)
When Valdorian household incomes rise, people buy fewer packets of the cheapest instant noodles at every price. Which statement is correct?
- (A) The noodles are an inferior good, and the demand curve for them shifts left.
- (B) The noodles are a normal good, and the demand curve for them shifts right.
- (C) The noodles are an inferior good, and buyers move up along the demand curve.
- (D) The noodles are a normal good, and the demand curve for them shifts left.
Answer and explanation
Answer: (A). Higher income leads to less bought at every price, so demand decreases (shift left). A good whose demand falls when income rises is an inferior good.
- (B) gets both parts wrong. Demand for a normal good would increase with income, but these buyers buy less.
- (C) names the good correctly but describes a movement along the curve. Only a change in the noodles’ own price causes a movement. Income shifts the curve.
- (D) has the right shift but the wrong label. For a normal good, higher income increases demand.
Question 3 (multiple choice · core)
Printers and ink cartridges are complements. The price of printers in Valdoria rises sharply. What happens in the market for ink cartridges?
- (A) Demand for ink cartridges decreases: the demand curve shifts left.
- (B) Demand for ink cartridges increases: the demand curve shifts right.
- (C) The quantity demanded of ink cartridges falls, shown as a movement up along their demand curve.
- (D) Nothing changes in the ink market, because the price of ink cartridges has not changed.
Answer and explanation
Answer: (A). Fewer people buy printers at the higher price, and people without printers do not need ink. So buyers want fewer cartridges at every price of ink: demand for ink decreases.
- (B) treats the goods as substitutes. A higher price of a substitute would increase demand, but printers and ink are used together.
- (C) would be right only if the price of ink had risen. The price that changed is the price of a related good, which shifts the ink demand curve.
- (D) ignores the fact that the price of a related good is a determinant of demand. The ink price is unchanged, but the whole curve moves.
Question 4 (multiple choice · core)
The table shows the weekly demand for bags of rice at one Valdorian market before and after an event.
| Price per bag | Quantity demanded before | Quantity demanded after |
|---|---|---|
| VD 10 | 400 | 550 |
| VD 12 | 300 | 450 |
| VD 14 | 200 | 350 |
| VD 16 | 100 | 250 |
Which event could explain the change?
- (A) Buyers hear that a poor harvest will make rice more expensive next month.
- (B) The price of a bag of rice falls from VD 14 to VD 10.
- (C) The price of bread, a substitute for rice, falls.
- (D) Several large families move away from the area.
Answer and explanation
Answer: (A). At every price, 150 more bags are demanded, so demand has increased (shift right). Expecting a higher price in the future makes buyers buy more now.
- (B) is a change in rice’s own price. It would be a movement along the “before” schedule (from 200 to 400 bags), not a new schedule.
- (C) A cheaper substitute makes buyers switch away from rice, so demand would decrease.
- (D) Fewer buyers would decrease demand, not increase it.
Question 5 (calculation · core)
A small Valdorian town has 40 identical cinema-goers. Each one’s weekly demand for cinema tickets is:
| Price per ticket | Tickets demanded by one buyer |
|---|---|
| VD 4 | 3 |
| VD 6 | 2 |
| VD 8 | 1 |
(a) Calculate the town’s market demand schedule. (b) A new housing estate brings 10 more identical cinema-goers. Calculate the new market demand schedule. (c) At a price of VD 6, by how much does the market quantity demanded change in (b)? Is this a change in demand or a change in quantity demanded? (d) With 50 buyers, the price rises from VD 4 to VD 8. What happens to the quantity demanded, and how is this shown on a graph?
Worked solution
(a) Multiply each buyer’s quantity by 40 at each price: VD 4: 40 × 3 = 120; VD 6: 40 × 2 = 80; VD 8: 40 × 1 = 40 tickets a week.
(b) Multiply by 50: VD 4: 150; VD 6: 100; VD 8: 50 tickets a week.
(c) At VD 6, quantity demanded rises from 80 to 100, an increase of 20 tickets. This is a change in demand (an increase): the number of buyers is a determinant, so the whole curve shifts right. The quantity rises at every price, not only at VD 6.
(d) Quantity demanded falls from 150 to 50 tickets, a fall of 100. This is a decrease in quantity demanded: a movement up along the new demand curve, because only the ticket price changed.
Suggested mark points (4): 1 for the schedule in (a); 1 for the schedule in (b); 1 for +20 and identifying a change in demand (shift right); 1 for the fall from 150 to 50 described as a movement along the curve.
Question 6 (constructed response · core)
Consider the weekly market for mango juice in a Valdorian city.
(a) Draw a correctly labelled graph of the demand for mango juice. Label the original demand curve D₁. (b) A widely reported study says mango juice is good for your health. On your graph, show the effect on the demand for mango juice. Label the new curve D₂. (c) Explain why your answer to (b) is a change in demand and not a change in quantity demanded. (d) Suppose instead that the price of mango juice falls and nothing else changes. Describe how you would show this on a graph that has only D₁. (e) Suppose instead that the price of orange juice, a substitute, falls. State what happens to the demand for mango juice, and explain why.
Model answer and suggested Marlbridge rubric
(a) Vertical axis labelled Price (VD per bottle); horizontal axis labelled Quantity (bottles of mango juice per week). A downward-sloping curve labelled D₁.
(b) A second downward-sloping curve D₂ drawn to the right of D₁, with an arrow from D₁ to D₂. Health news changes tastes and preferences in favour of mango juice, so buyers want more at every price.
(c) The price of mango juice has not changed. A determinant (tastes) has changed, so buyers want a larger quantity at every price. That moves the whole curve, which is a change in demand. A change in quantity demanded happens only when the good’s own price changes.
(d) Mark a point on D₁ at the original price and a second point lower down and to the right on the same curve at the lower price. Show the movement with an arrow along D₁. Quantity demanded rises; the curve does not shift.
(e) Demand for mango juice decreases (the curve shifts left). Orange juice is now relatively cheaper, so some buyers switch from mango juice to orange juice and buy less mango juice at every price.
| Point | What earns it |
|---|---|
| 1 | Correctly labelled axes (price and quantity) and a downward-sloping D₁ |
| 1 | D₂ drawn to the right of D₁ and labelled |
| 1 | Explains that the price is unchanged and a determinant (tastes) has changed, so quantity rises at every price |
| 1 | Movement along D₁ to a lower price and higher quantity, with no shift |
| 1 | Demand for mango juice decreases, with the switch to the cheaper substitute as the reason |
In (b), an arrow is good practice; if the curve is clearly to the right and labelled D₂, accept it without the arrow. In (e), “decreases” with no reason does not earn the point.
Question 7 (constructed response · stretch)
Electric scooters are a normal good in Valdoria. Bus rides are a substitute for scooters. In the same year, two things happen: average incomes rise, and the government cuts bus fares.
(a) Explain the effect of each event on its own on the demand for scooters. (b) Can you be sure whether the demand for scooters increases or decreases overall? Explain. (c) A study finds that, at a scooter price of VD 900, the income rise alone would shift demand so that 300 more scooters a year are demanded, and the fare cut alone would shift it so that 120 fewer are demanded. Before both events, 1,000 scooters a year were demanded at VD 900. Calculate the new quantity demanded at VD 900 and state the overall direction of the shift. (d) A newspaper writes: “Scooter prices fell last year and sales rose, which proves that the demand for scooters increased.” Explain the error in this reasoning.
Model answer and suggested Marlbridge rubric
(a) Higher income increases demand for scooters (shift right), because scooters are a normal good. Cheaper bus fares make the substitute relatively cheaper, so some people take the bus instead: demand for scooters decreases (shift left).
(b) No. The two events push the curve in opposite directions. The overall direction depends on which effect is larger, so without more information it is indeterminate.
(c) New quantity demanded at VD 900 = 1,000 + 300 − 120 = 1,180 scooters a year. The net change is +180, so the demand curve shifts right overall: demand increases.
(d) A fall in the scooters’ own price raises the quantity demanded: a movement down along the existing demand curve. Higher sales after a price fall are exactly what the law of demand predicts, even if the curve did not move at all. So the evidence does not prove that demand increased; that would need buyers to want more scooters at every price.
| Point | What earns it |
|---|---|
| 1 | Income rise increases demand because scooters are normal |
| 1 | Fare cut decreases demand because the substitute is relatively cheaper |
| 1 | Overall effect indeterminate without knowing the sizes of the two effects |
| 1 | 1,180 scooters and a net shift to the right |
| 1 | Identifies that a price fall causes a movement along the curve (change in quantity demanded), not a shift |
In (b), a student who states “it depends on the relative size of the two shifts” earns the point. In (c), accept “an increase in demand of 180 at VD 900” as the direction.
How did you do?
- Q1, Q5(d), Q6(d) or Q7(d) wrong: re-read “Change in quantity demanded v. change in demand” and Worked example 1 in the study guide.
- Q2, Q3, Q4, Q6(e) or Q7(a) wrong: re-read “The determinants of demand” and its summary table.
- Q5(a)–(c) wrong: revisit how market demand is built in Worked example 1 (add quantities at each price).
- Q6(a)–(b) wrong: compare your graph with Figures 1 and 2 and the graph checklist in the revision notes.
- Q7(b)–(c) wrong: revisit Worked example 2, where two separate shifts are compared at the same price.
Then tick off the topic checklist.