Final answer:
Ramen noodles with an income elasticity of demand of -4 are an inferior good, meaning demand decreases as income increases. Other goods have their own elasticities, potentially as normal goods, which have a positive elasticity and are divided into necessities (<1) and luxuries (>1).
Step-by-step explanation:
If the income elasticity of demand for ramen noodles is calculated to be -4, this indicates that ramen noodles are an inferior good. Income elasticity of demand measures the responsiveness of the quantity demanded of a good to a change in income. A negative income elasticity indicates that as income increases, the demand for the good decreases, which is characteristic of inferior goods.
The income elasticity of demand for other goods is not determined by the elasticity of ramen noodles. Each good has its own income elasticity that can vary independently. However, when a person's income increases, they might decrease their consumption of inferior goods like ramen noodles and instead increase their consumption of normal goods, which have a positive income elasticity of demand.
Economists define normal goods as having a positive income elasticity. Within normal goods, those with an elasticity less than one are referred to as necessities, while those with an elasticity greater than one are known as luxuries. Necessities are essential items that we need regardless of income changes, whereas luxuries are non-essential goods that we may buy more of as our income increases.