4.1 Charity events often use silent auctions. A donated item, such as a date with a movie star (Colin Firth and Scarlett Johansson in 2008) or a former president

(Bill Clinton in 2013), is put up for bid. In a silent auction, bidders write down bids and submit them. Some silent auctions use secret bids, which are submitted in sealed envelopes and kept confidential. Other silent auctions are open: the bidder writes down a bid on a bulletin board that everyone present can see. Which kind of auction would you expect to raise more revenue for the charity?