In the key of C the scale is C,D,E,F,G,A,B,C The I, IV and V chords are built on the 1st, 4th and 5th notes of that scale - chords C,F and G. The relative minor in the key of C is Am. A is the 6th note in the C major scale and the Am chord consists of A, C and E (built on the 6th note of the minor scale). This applies in every key. List the 7 notes in any key and the relative minor will be built on the 6th note of that scale. e.g. Key of D Notes: D,E,F#,G,A,B, C# Relative minor in D is Bm here again built on the 6th note of the major scale. Hope this helps.