The easy's way to understand all this is to look at the root note as home base. The 1st ,4th and 5th are major chords every other chord in that scale will be a minor chord. This will apply to every key of the major scale. In the minor scales it will be 1st, 4th , 5th as a minor chord, all the other chords will be major. I hope this helps someone. It's the way I taught myself to remember it.