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Quantitative aptitude · lesson 11 of 30 · free

Percentage increase and decrease — Quantitative aptitude for kids

Prices rise, populations grow, water gets used up. Percent change compares the change with the starting value. When one change comes after another, the second works on the new value — so +20% then −10% is not +10%.

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The method

Start value is 100% — “percent change is always worked out on the value before the change”

  1. New value after a rise of p%: value + p% of value. After a fall: value − p% of value.
  2. Percent change = change ÷ starting value × 100.
  3. Two changes a% and b% one after the other: a + b + (a × b) ÷ 100, with a fall counted as minus.

Use it for: Price changes, salary rises, population growth, marks going up or down, and data interpretation.

🧮 Check your own sums with the free Percentage calculator — it shows the working.

Worked example: A price goes up by 20% and then comes down by 10%. By what percent has it gone up in all? → 8

  1. Use a + b + (a × b) ÷ 100 with the fall as minus: 20 − 10 − (20 × 10) ÷ 100.
  2. 20 − 10 − 2 = 8.

Check: ₹100 → ₹120 → ₹108: it went up by 8% ✓

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✓ Written and checked by the TalentJR team · Updated 13 Oct 2026 · How we make our lessons

✏️ Practice

Work it out in your head or on paper, then tap your answer — or type it and press Check. Stuck? Press “Show me how”.

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🏁 Lesson 11 test

20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.

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🖨️ Percentage Increase and Decrease Worksheet

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