query for decade using a date field

[MikeHenson]

I am working on a neighborhood map. I have subdivisions shown, and each subdivision has a "platdate" field within my subdivision shape file. I am wanting to categorize the subdivisions by the decade they were built. Can someone show me how to run a query to do this? Thanks for any help you can give.

[MikeHenson]

to add to this request, I dont even have to have an actual query, but just display they symbology in different colors for each decade.