Data Point: 21

The average life span in months for a $1 bill.   The U.S. Mint, as directed by the Presidential $1 Coin Act of 2005, is promoting the use of dollar coins as a green alternative to the greenback. The mint says dollar coins last decades and that their use could save the government billions of dollars over many years. The Mint has minted more than 1 billion of the new presidential dollar coins since January 2007. Four designs are minted each year, honoring the presidents in the order in which they served.   Source: Bureau of Engraving and Printing, www.moneyfactory.gov; U.S. Mint, www.usmint.gov.