1. Let's start by understanding the problem: calculating percentage increase or decrease, or both in the same problem. 2. The formula for percentage increase is: $$\text{Percentage Increase} = \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \times 100\%$$ This tells us how much a value has grown compared to the original. 3. The formula for percentage decrease is: $$\text{Percentage Decrease} = \frac{\text{Original Value} - \text{New Value}}{\text{Original Value}} \times 100\%$$ This tells us how much a value has reduced compared to the original. 4. Important rules: - If the new value is greater than the original, it's an increase. - If the new value is less than the original, it's a decrease. 5. When both increase and decrease happen in the same problem, calculate each step separately using the formulas above. 6. Example: Suppose a price increases from 100 to 120, then decreases to 90. - First increase: $$\frac{120 - 100}{100} \times 100\% = 20\%$$ increase. - Then decrease: $$\frac{120 - 90}{120} \times 100\% = 25\%$$ decrease. 7. Always use the immediate previous value as the original value for the next calculation. This method helps you calculate percentage changes clearly and accurately.