Final answer:
The value of cross elasticity of demand between substitutes like orange soda and grape soda is generally positive because an increase in the price of one leads to an increase in demand for the other.
Step-by-step explanation:
The value of the cross elasticity of demand between orange soda and grape soda is positive if the goods are substitutes, which means that an increase in the price of one will lead to an increase in the quantity demanded for the other. However, if the number is negative, these two goods are complements, which means that an increase in the price of one leads to a decrease in the quantity demanded for the other. In the example given, the cross-price elasticity is demonstrated by the change in demand for apples as the price of oranges changes.
The formula % change in Qd for apples / % change in P of oranges shows the relationship. The given example implies a positive cross elasticity of demand, which is 0.4 when the price of oranges falls by 3% leading to a 1.2% decrease in the demand for apples. Nevertheless, as this is not the exact scenario the student inquires about (which is between orange soda and grape soda), we can't apply this example to respond to the question directly without additional information regarding the relationship between orange soda and grape soda.
If orange soda and grape soda are substitutes, we would expect the cross elasticity to be positive as an increase in the price of one leads to an increase in the demand for the other. The correct answer, given no other information, is positive.