How Long is a Decade
How long is a decade? answer: A decade is 1/10th of a century. Oh, you say you don't know how long a century is either? Ok, then a decade is 10 years. Want to know how long a century is - look it up. :)
A decade is a period of 10 years. In contract, a century is a period of 100 years, while a millenium is a period of 1000 years. 2010 was the start of a new decade in the USA.