According to macroeconomic theory, for a single-price monopoly, marginal revenue is positive when demand is elastic and is negative when demand is inelastic.
When the demand is elastic, reducing the price and selling more units results in total revenue increasing.
Therefore, to make this valid, Marginal Revenue must be greater than 0.
On the other hand, when demand is inelastic, reducing the price and selling more units decreases total revenue.
Thereby, to make this valid, Marginal revenue must be less than 0.
Hence, in this case, it is concluded that the correct answer is positive and negative, respectively.
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