According to the midpoint formula, how is the percentage change in quantity calculated?

The midpoint formula for calculating the percentage change in quantity is correctly represented by the choice that involves dividing the change in quantity by the average quantity. Specifically, the formula is structured as follows:

When calculating the percentage change in quantity, we take the difference between the new quantity and the old quantity—this represents the change in quantity. Then, instead of simply dividing by the old quantity, we use the average of the old and new quantities to provide a more balanced perspective on the change. This average is computed as (Qnew + Qold) / 2.

Using this method helps avoid biases that can arise from using only the old or new value, particularly when the values are substantially different. By employing the average quantities in the denominator, the midpoint formula yields a more accurate reflection of the relative change in quantity. This approach is especially useful in economics to ensure clarity and consistency when calculating elasticities or other percentage changes.