The below progression is exactly the same as the previous one, except that it is now in the key of A. That means that instead of using E7-A7-B7 as our I-IV-V, we are now using A7-D7-E7.

With only four chords, you can now play along with hundreds of blues songs!!! Aren't you sorry that you wasted time learning your major chords before learning your seventh chords?