a. Economics seeks to interpret, analyze and or evaluate situations that occur between individuals, firms and other entities. Due to the potential for multiple agents and other known and unknown external activities to be involved or present but not relevant to an analysis, economics employs the assumption of 'ceteris paribus' in the law of demand, with the help of diagram enumerate the types of elasticity of demand.
b. The relation amidst percentage change in quantity to percentage change in price of a related commodity is termed as cross elasticity of demand. J.S. Sloman, defines as "Cross elasticity of demand refers to the responsiveness of demand for one good to a change in the price of another." All the elasticities are worked out in terms of percentage or proportional change in dependent variable (demand) to a given percentage or proportional change in the independent variable (price of the commodity, income of the consumer, and prices of other commodities). Exemplify the cross and income elasticity of demand with suitable examples.