This tool lets you pick a short story about a fictional coconut drink market, choose what you think happens to the curves, and see the model answer. It draws a labelled diagram, lists the same numbers in a table and gives a checklist for writing the explanation.
Free tool · Economics
Supply and demand reasoning explorer
You can draw the shift but cannot explain in words why price changes.
Everything you enter stays on this device.
It helps students who can sketch demand and supply lines but struggle to say why the price or quantity changes.
How do I use it?
- Pick one of the scenarios.
- Choose the movement you think fits: demand or supply shifting right or left, or a price set away from equilibrium.
- Set the size of the shift, or the price if you chose the price option.
- Press “Show the model”, compare your choice with the reviewed answer, then write your own explanation before opening the model explanation.
How does it work?
The model is fixed: demand is Qd = 120 − 4P and supply is Qs = 20 + 6P, with P in RM and Q in drinks a day. Setting Qd equal to Qs gives the original equilibrium of RM10 and 80 drinks.
A shift adds or subtracts your chosen amount at every price on one curve, then the tool solves for the new equilibrium. It also reports the shortage or surplus at the old price, which is the reason the price moves.
The price option moves no curve. It reads quantity demanded and quantity supplied at the price you set and reports the gap, so you can see that a surplus or shortage is not a shift.
A short worked example
Suppose demand rises by 40 drinks at every price, with supply unchanged. The new demand curve is Qd = 160 − 4P.
At the old price, the model gives quantity demanded 120 and quantity supplied 80, a shortage of 40. Setting 160 − 4P equal to 20 + 6P gives RM14 and 104 drinks.
Price and quantity both rise. Quantity supplied increases along the supply curve, which did not move.
What are its limits?
The curves are straight lines with stated numbers, and only one change is tested at a time. It is a classroom model, not a prediction of real prices and not a recommendation about any policy.
The tool checks your choice of movement. It does not mark your written explanation, which stays on your device.
Where does it connect to the lessons?
The tool supports the demand and supply lessons in the SPM Economics hub. Use it with the study guides on explaining an economics diagram in words and distinguishing needs, wants and resources.
If explaining diagrams in words is where marks slip, SPM Economics tuition gives you a teacher to practise with you. It starts with the one-hour trial class (from RM50).
Common questions
What is the difference between a shift and a movement along a curve?
A change in the good's own price moves you along the same curve. A change in a non-price factor, such as tastes, income or production cost, moves the whole curve to a new position. The tool has a separate option for each.
Why does the tool use one fixed market?
A fixed model with stated numbers lets every answer be calculated and checked. The same reasoning applies to other markets, but the actual figures here belong to the classroom model and not to any real product.
What does ceteris paribus mean in an answer?
It means all other factors stay the same, so only the one change you are studying affects the result. Stating it shows your reader that you are isolating one cause at a time.
Can this tell me what will happen to real prices?
No. It is a classroom model with straight-line curves and one change at a time. Real prices depend on many factors together, so use the tool to practise reasoning, not to forecast.
A teacher working one-to-one can listen to how you explain a diagram, point out where a step is missing, and practise the wording with fresh scenarios until it comes out clearly.
- Online one-to-one lessons for your child with an experienced teacher.
- Your first class is a one-hour trial, from RM50. The fee is agreed before you book.
- Happy with the teacher? Continue with lessons of about 1.5 hours. If not, ask for another teacher.