"nina hired sue to work as a janitor in nina's apartment building. sue was negligent in that she left a crack in the marble staircase unrepaired, without putting up a warning sign. seth slipped on the staircase and suffered severe injuries. who is liable for this accident? "

I would saythat if Nina new about the crack and knowingly took no remedial action like putting up a warning sign or having it repaired, then she would be liable but if Sue didn't tell Nina about the danger of the crack, and urged her to take action to fix it, then she would be liable.

the combined consumer and producer surplus is maximized.

Explanation:

Allocative efficiency occurs when the production in the economy is aligned with the consumer preferences. Here, the particular mix of the products that the society produces consist of what the society desires.

When a competitive market achieves allocative efficiency, the combined consumer and producer surplus is maximized.