According to the beginner guide, to setup the ADT Plugin, one of the procedures is
http://developer.android.com/sdk/eclipse-adt.html#installing
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Late to the conversion...
For me, I found this at:
C:\Program Files (x86)\Android\android-sdk
This is the default location for Windows 64-bit.
Also, try to recall some of your default locations when not presented with some suggestions.