So follow through the years, what was the last day of the first century?

If that's so, then the first decade was only 9 years? Now think about it and start over because there was no year 0.

Continue through the years, what was the last day of the first millenium?

You're math is wrong, you're century only had 99 years, start over.

Good. Now keep going. What was the last of the second millenium?

Check you're math again, you're millenium only had 999 years, start over.

Great, continue a little more. What was the last day of the first decade of the second millenium?

Once again, check you're math, you're second millenium only had 999 years. Start over.

AWESOME! Just go a little backwards. If that was the last day of the first decade of the second century, then wouldn't that mean 2010 is part of the 2000's decade?

One last time, check you're math and start over (you know why).