Why this is mistaken
Slope divides changes in original units. Elasticity divides proportional changes and is unit-free. A linear curve can have a constant slope while its elasticity changes along the line because the price and quantity bases change.
Repair the work by naming response and driver, computing each endpoint average, dividing each change by its matching average, and then dividing the two proportional changes. Retain the slope only when the question actually asks for quantity units per price unit.
Where to watch
When this mistake may appear
- Two price-quantity points are supplied.
- Responsiveness is compared across products with different units or scales.
Check your work
Your work may contain this mistake if:
- Reports -10 chairs per dollar as an elasticity of -10.
- Divides raw quantity change by raw price change but calls the answer unit-free.
- Uses a start-base percentage in one direction and treats the reversed result as a different relationship.