If the number of subway rides that Mary demands increases from 4 per week to 5 per week when her income increases from $50,000 to $75,000 per year, what is Mary’s income elasticity of demand for subway rides? What type of good are subway rides for Mary? If the number of subway rides that Mary demands increases from 4 per week to 5 per week when her income increases from $50,000 to $75,000 per year, what is Mary’s income elasticity of demand for subway rides? What type of good are subway rides for Mary?