What key is Rock and Roll, Hoochie Koo in?

Rock and Roll, Hoochie Koo is based on the A minor pentatonic scale and A minor scale (natural minor or Aeolian mode).

The intro uses the chords F5 G5 A5 and then a C5. This chord movement is very common and stems from a 4 5 6 chord progression in the A natural minor scale (Aeolian mode, C major scale). But only power chords are played (if you listen closely you can hear that a 6th interval is added to the F5 and G5 giving it a blues shuffle style). Instead of using the full minor scale over these changes the guitars mainly stick to A minor pentatonic (as heard in the riff at the end of the chord figure).

The E7 (0:28 in the video) is technically a key change, but you could treat it like a blues 5 chord and continue playing A minor pentatonic over it. You could think of it as the 5 chord in the key of A major and play A major scale patterns over it. You could treat it as a blues key change and play a mixture of E major and E minor pentatonic scales over it. Or it could possibly be thought of as a 5 (V7) chord in A harmonic minor (but this might sound a bit too exotic for this bluesy rock song). Or you could not play over it at all, as is the case in the song.

The verse (0:51 in the video) uses the chords A5 C5 D5. Again, these power chords still stem from the A natural minor scale (Aeolian mode, C major scale). All of these notes are also found in the A minor pentatonic. The guitar riff that occurs after each line of the verse is the A minor pentatonic with a chromatic passing tone added (blues scale). See guitar tab below.

Verse Riff: A Minor Pentatonic "Blues" Scale Patterns 3 & 4
E----------------------|------------------|
B----------------------|------------------|
G------14--14-12-------|----------12b(14)-|
D----------------14-13-|-12-10------------|
A--12------------------|------------------|
E----------------------|------------------|


So you can see that Rock and Roll, Hoochie Koo is based on minor chord progressions and pentatonic scale patterns. This is very common in blues and blues-based rock songs.