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15 Flashcards in this deck.
A percentage represents a part of a whole expressed out of 100. It is a way to describe proportions and ratios in a standardized manner. The symbol for percentage is %. Understanding percentages is essential as they provide a basis for calculating percentage increase and decrease.
Percentage increase refers to the amount by which a value grows relative to its original value, expressed as a percentage. It is commonly used to measure growth in various contexts such as population growth, price hikes, and income increments.
The formula to calculate percentage increase is: $$ \text{Percentage Increase} = \left( \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \right) \times 100\% $$
Example:
If the price of a book increases from $50 to $60, the percentage increase is:
$$
\text{Percentage Increase} = \left( \frac{60 - 50}{50} \right) \times 100\% = 20\%
$$
Percentage decrease is the amount by which a value reduces relative to its original value, expressed as a percentage. It is widely used to determine discounts, depreciation, and decreases in population or sales.
The formula to calculate percentage decrease is: $$ \text{Percentage Decrease} = \left( \frac{\text{Original Value} - \text{New Value}}{\text{Original Value}} \right) \times 100\% $$
Example:
If the salary decreases from $4000 to $3500, the percentage decrease is:
$$
\text{Percentage Decrease} = \left( \frac{4000 - 3500}{4000} \right) \times 100\% = 12.5\%
$$
Percentage increase and decrease have numerous applications across different fields:
Sometimes, values undergo multiple percentage increases or decreases over time. Compound percentage changes consider sequential percentage alterations on a value.
The formula for compound percentage change over multiple periods is: $$ \text{Final Value} = \text{Original Value} \times \left(1 \pm \frac{\text{Percentage Change}_1}{100}\right) \times \left(1 \pm \frac{\text{Percentage Change}_2}{100}\right) \times \dots \times \left(1 \pm \frac{\text{Percentage Change}_n}{100}\right) $$
Example:
If a population increases by 10% the first year and then decreases by 5% the second year, the final population is:
$$
\text{Final Population} = P \times 1.10 \times 0.95 = P \times 1.045
$$
This represents an overall increase of 4.5%.
Students often make errors when calculating percentage increases and decreases. Here are common pitfalls and how to avoid them:
Applying percentage increase and decrease to real-world problems enhances understanding. Consider the following problem:
Problem:
A school's enrollment increased from 800 students to 920 students in one year. Calculate the percentage increase in enrollment.
Solution:
Using the percentage increase formula:
$$
\text{Percentage Increase} = \left( \frac{920 - 800}{800} \right) \times 100\% = \left( \frac{120}{800} \right) \times 100\% = 15\%
$$
Therefore, the school's enrollment increased by 15%.
Understanding percentage increase and decrease is interconnected with other mathematical concepts such as ratios, proportions, and decimals. Mastery of these interrelated topics enhances problem-solving skills and mathematical proficiency.
Aspect | Percentage Increase | Percentage Decrease |
Definition | Growth of a value relative to its original value. | Reduction of a value relative to its original value. |
Formula | $$\left( \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \right) \times 100\%$$ | $$\left( \frac{\text{Original Value} - \text{New Value}}{\text{Original Value}} \right) \times 100\%$$ |
Application Examples | Salary increments, population growth. | Discounts, depreciation of assets. |
Impact on Original Value | Increases the original value. | Decreases the original value. |
Common Mistakes | Using incorrect base value. | Misapplying the decrease formula. |
Remember the acronym “POUND” to avoid common mistakes:
Did you know that compound percentage changes can significantly impact long-term financial growth? For instance, investing $1,000 with an annual growth rate of 5% will grow to approximately $1,628 after 10 years due to compound interest. Additionally, during the Great Depression, the U.S. stock market experienced a drastic percentage decrease of nearly 90%, illustrating the profound effects of percentage changes on economies.
1. Using the New Value as the Base: Students often mistakenly use the new value instead of the original value when calculating percentage changes.
Incorrect: $$\left( \frac{\text{New Value} - \text{Original Value}}{\text{New Value}} \right) \times 100\%$$
Correct: $$\left( \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \right) \times 100\%$$
2. Ignoring the Direction of Change: Mixing up percentage increase and decrease leads to incorrect results.
Incorrect: Using the increase formula when a decrease is involved.
Correct: Apply the percentage decrease formula for reductions.