If a company's total costs per day increase from $200 to $400 by adding another worker, but its additional benefits are $300, it is sensible to add that additional worker

If perfectly competitive firms are making an economic profit, the economic profit

A) attracts entry by more firms, which lowers the price. B) can be earned both in the short run and the long run. C) is less than the normal profit. D) leads to a decrease in market demand. E) generally leads to firms exiting as they seek higher profit in other markets.

Explain why the marginal propensity to save and the marginal propensity to consume sum to 1