531441/524288. (Or its reciprocal; this is a bit tricky. 531441/524288 is the interval from C to the B♯ below it, which cannot be represented easily as an interval: augmented zeroth?! Anyway, by size, it’s a diminished second.)
AAAAAAA3. It’s a septuple augmented third, minus an octave. Yes. Above C, it would be written as a major third with seven sharps. Yikes.
Exercise 2
−1, −4.
513/512.
+1.
Exercise 3
M65, m35, m37, m75.
10/9, 9/7, 11/6.
No. It would be the sixth mode if the fourth degree of the scale was F5 instead of F. The two scales are actually built on tonic, subdominant, and dominant triads of 4:5:6 (5/4 major) and 10:12:15 (6/5 minor) respectively. The scale with 3 major triads contains only 2 minor triads, and the scale with 3 minor triads contains only 2 major triads.
Exercise 4
m27, A2513, d41125.
12/7, 13/10, 243/200.
The following five chords:
I chord: 1/1, 3/2, 5/4, 1/1
vi chord: 5/3, 5/3, 5/4, 1/1
ii chord: 4/3, 5/3, 4/3, 10/9
V chord: 3/2, 3/2, 9/8, 15/8
I chord: 1/1, 3/2, 5/4, 1/1
P155. The interval is 440/432 = 55/54. Please don’t buy into 432 Hz stuff, thanks.