Final answer:
Good X and good Y are substitute goods because the cross-price elasticity of demand is positive, indicating that an increase in the price of good Y leads to an increase in the demand for good X.
Step-by-step explanation:
The relationship between good X and good Y can be determined by looking at the cross-price elasticity of demand. In this case, the cross-price elasticity of demand for good X is 2.5, which suggests a positive relationship with good Y. Because the cross-price elasticity is positive and the price of good Y has increased by 25%, this indicates that good X and good Y are substitute goods. People will tend to purchase more of good X when the price of good Y goes up.