When her income falls from $50,000 to $20,000, Alex increases her monthly purchase of hamburger from 20 pounds to 35 pounds. Using the midpoint method, Alex's income elasticity of demand for hamburgers is:
|-1.57| or 1.57
|-0.63| or 0.63
|0.54| or 0.54
|-0.85| or 0.85
Cannot be calculated from this information