Women and numbers don't mix
However, in this case they seem to be right from what you're saying. Mostly. If we started in year '1', then '10' is the last year of the decade, and so it must be completed before the decade is through.

We all agree that a decade is 10 years (I hope). If I owed you say, a decade of pounds (£10 for anyone feeling a bit slow this morning), and I gave you £9 as I was counting 'pound zero', you'd probably be pretty hacked off. So, here it is:

Decade 1: 1 2 3 4 5 6 7 8 9 10

Decade 2: 11 12 13 14 15 16 17 1 19 20

...

[Edit: Decade 200: 1991 1992 1993 1994 1995 1996 2997 1998 1999 2000 - 2000 is the tenth year of this decade]

Decade 201: 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

All years in each decade must be completed before the decade is over. Then again the whole thing's an arbitrary system of measuring time invented by man, so to be honest who gives a fuck whether it's the new decade or not.
( greedyostrich Cheese is evil! Cheddar is VOODOO!, Fri 1 Jan 2010, 12:16, 1 reply)

I agree with your maths
The Third Millennium started on 1 January 2001. So did the 21st Century. I get annoyed at people who don't realise this.

So did the 201st decade.

BUT... people very rarely talk about the "Nth decade", but instead refer to decades (groups of ten years) by the first 3 digits (1920s, 1980s etc.).

So, 1 January 2010 is the start of the "Twenty Tens", and 1 January 2011 will be the start of the less famous 202nd decade.
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Sat 2 Jan 2010, 16:49, closed)