1. Let's start by understanding what percentage increase and decrease mean. 2. Percentage increase is used when a value goes up. The formula is: $$\text{Percentage Increase} = \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \times 100\%$$ 3. Percentage decrease is used when a value goes down. The formula is: $$\text{Percentage Decrease} = \frac{\text{Original Value} - \text{New Value}}{\text{Original Value}} \times 100\%$$ 4. Important rules: - Always subtract the original value from the new value for increase. - For decrease, subtract the new value from the original value. - Divide by the original value to find the fraction of change. - Multiply by 100 to convert to a percentage. 5. Example for increase: If a price goes from 50 to 60, $$\text{Percentage Increase} = \frac{60 - 50}{50} \times 100\% = \frac{10}{50} \times 100\% = 20\%$$ 6. Example for decrease: If a price goes from 80 to 60, $$\text{Percentage Decrease} = \frac{80 - 60}{80} \times 100\% = \frac{20}{80} \times 100\% = 25\%$$ 7. So, percentage increase and decrease help us understand how much a value has changed relative to its original amount.