Price rises from $20 to $25 and quantity demanded falls from 100 to 80. Using the original values as the base, PED equals:

解說

%ΔQd = −20/100 = −20%. %ΔP = 5/20 = +25%. PED = −20/25 = −0.8. Option C drops the sign. Option B inverts the ratio. Option D divides by 5 instead of by the percentage change in price.