Percentages do not add up, and that costs people money
This is the single most common percentage mistake, and it is not an obscure one. A stock rises 20% and then falls 20%: most people read that as breaking even. It is not. Starting at ₹100, the rise takes you to ₹120, and a 20% fall from ₹120 is ₹24 — leaving ₹96. You are 4% down.
The reason is that each percentage is measured against whatever the value was at that moment, not against where it started. The base moves, so the percentages multiply rather than add. Three successive 10% discounts are 27.1% off, not 30%. A 50% pay cut needs a 100% rise to undo.
Every percentage calculator on the first page of search results handles one change at a time. The chain mode here handles as many as you like, and shows the gap between the real answer and the one your intuition gives — because the gap is the whole point.