中等ECON-ELAS-020
Income rises by 10% and quantity demanded of a good rises by 4%. Income elasticity is:
A. 2.5, so the good is inferior.
B. −0.4, so the good is inferior.
C. 4, because the quantities are 4 and 10.
D. 0.4, so the good is normal and income-inelastic.✓ 答案
解說
YED = %ΔQ / %ΔY = 4/10 = 0.4. Positive YED means normal. Below 1 means income-inelastic: demand rises less than proportionally with income. Inverting the ratio or forcing a minus sign changes the good’s type.