Alessandra won an auction where her bid price was $25, and the second highest price was $24. How much will she pay?

Alessandra will pay $24.01. This scenario describes a second-price auction (also known as a Vickrey auction), which is common in online advertising. In a second-price auction, the winner pays a small increment above the second-highest bid. This mechanism encourages bidders to bid their true valuation for the ad space. If she paid $24, it would be the exact second-highest bid, which is not how these auctions typically resolve. Paying $25 would mean she paid her maximum bid, which is incorrect for a second-price auction. $24.50 is an arbitrary amount between the two bids and doesn't reflect the standard auction rule.