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11
(10+12)/2.
Class 9 · English Version · Economics
Markets, demand and supply
Compare an initial-base elasticity with a midpoint measure.
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Learn the idea
Price elasticity compares proportional quantity change with proportional price change. An initial-base calculation depends on direction; the midpoint method divides each change by the average of its starting and ending values. Neither calculation establishes causation by itself.
Worked example
Price10→12 and quantity100→80 give initial-base elasticity−20%/20%=−1. Midpoint quantity change−20/90 and price change2/11 give−11/9, about −1.22. Both describe this finite comparison with different bases.
- State the endpoints.
- Name each percentage base.
- Separate description from causal inference.
Your written practice
Show your working on paper and enter your answer here. If it does not match, compare the model and try again.
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90
(100+80)/2.
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3
30/10.
Write in your own words. A guardian or teacher should review this response.
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Different percentage bases can produce different finite-change values.
Name the bases, not an unexplained discrepancy.
Write in your own words. A guardian or teacher should review this response.
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Supply shifts or other simultaneous changes may influence both, so the demand relationship is not isolated.
Give a plausible alternative mechanism.
Apply the idea
Calculate both methods for a fictional change and explain each ratio in words.
Review with a guardian or teacher
- Use the stated evidence or givens.
- Show reasoning rather than only a result.
- Review and explain one correction.
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