How do you calculate percentage difference between two values?

• A. (|A - B|) / A × 100%
• B. ((A + B)/2) × 100%
• C. |A - B| ÷ B × 100%
• D. |A - B| / ((A+B)/2) × 100%

Answer: (D)

The measure being tested is the percentage difference, which treats two values symmetrically. To do this, use the absolute difference |A − B| and divide by the average of the two values, ((A + B) / 2), then multiply by 100. This base—the average—balances the two numbers so the result doesn’t depend on which value you pick as the reference.

For example, if A is 80 and B is 100, the difference is 20 and the average is 90, giving 20/90 ≈ 22.2%. If you used one value as the base instead (20/80 = 25% or 20/100 = 20%), you’d get different percentages, which shows why using the average base gives a true, symmetric difference.

This is different from percent change, which uses a specific starting value as the base (for instance, (B − A) / A × 100% for the change from A to B).