Answer:
The correct answer is option (a): If the price of peanuts is equal to the price of corn chips, then the marginal utilities must also be equal.
When a consumer is maximizing utility, the marginal utility per dollar spent on each good must be equal. This is because the consumer will allocate their spending in such a way as to maximize their overall utility. If the marginal utility per dollar spent on one good is greater than on the other, the consumer can increase their overall utility by shifting their spending towards the good with the higher marginal utility per dollar.
In the case where a consumer is spending all their income on two goods, the marginal utility per dollar spent on each good is equal to the ratio of the marginal utility of the good to its price. So, if the price of peanuts is equal to the price of corn chips, then the marginal utilities must also be equal.
Option (b) is incorrect because the marginal utility of a good is not directly related to its price. It is possible that the marginal utility of peanuts is greater than the marginal utility of corn chips, even if the price of peanuts is higher.
Option (c) is also incorrect for the same reason. It is possible that the marginal utility of peanuts is less than the marginal utility of corn chips, even if the price of peanuts is lower.
Option (d) is incorrect because, as explained above, the marginal utilities of the two goods and their prices are related through the concept of marginal utility per dollar spent.