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Mathematics·Percentages·grades 6–9

An item went up 20%, then down 20% — how did the price change?

Problem

The price of an item first rose by 20%, and then the new price fell by 20%. By what percentage does the final price differ from the original one?

Answer

The final price is 4% below the original one

Step-by-step solution

  1. Step 1. Denote the initial price

    Let the initial price be 100 (a convenient number — percentages are easier to compute). Everything else is expressed in terms of it.

  2. Step 2. An increase of 20%

    After the rise of 20% the price became 100⋅1.2=120100 \cdot 1.2 = 120.

2 more steps — unlocked after you sign in:

  • Step 3. A decrease of 20%
  • Step 4. Compare with the start
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Common mistakes

  • Assuming that +20% and −20% cancel each other out and the price does not change — that is wrong.

  • Taking the second percentage from the initial price instead of from the new one.

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