TEST n. 1 Cost Of Living

the correct answer is as you write y2-y3, but the calculus are wrong:

you have to make this calculus: (END_value - START_value )/START_VALUE

y0-y1 = 100 -> 95 is 5% of percentage decrease

y1-y2 = 95 -> 90 is 5,26% of percentage decrease

y2-y3 = 90 -> 85 is 5,55% of percentage decrease