Percent Increase & Decrease
Percent change = (amount of change / original amount) x 100 — the denominator is always the ORIGINAL (starting) value, not the new one.
For successive changes, apply each multiplier in turn: a 10% increase followed by a 10% decrease is 1.10 x 0.90 = 0.99 of the original — a net 1% decrease, not zero.