Percentage change formula for 7th grade math

➕ Percentage Change: What Is It?

Percentage change shows how much something has increased or decreased. It's the difference between the new value and the original value, expressed as a percentage of the original value.

📜 A Little History

The concept of percentages has been around for centuries, dating back to ancient Rome! They were initially used for calculating taxes and interest. Over time, percentages became a standard way to express proportions and changes in various fields, including mathematics, finance, and statistics. Nowadays, we use percentage change to analyze data, track trends, and make informed decisions in many aspects of life.

🔑 The Key Formula

Here's the magic formula you need to know:

Percentage Change = $\frac{\text{New Value - Original Value}}{\text{Original Value}} \times 100$

➗ Understanding the Parts

• 🆕 New Value: The final amount after the change.
• Old Original Value: The starting amount.
• 💯 Multiply by 100: This turns the decimal into a percentage.

🧮 How To Calculate

1. Calculate the difference: New Value - Original Value
2. Divide the difference by the Original Value
3. Multiply the result by 100
4. Add a "%" sign at the end

🌍 Real-World Examples

🍬 Candy Price Hike

Let's say a candy bar used to cost $1.00, and now it costs $1.25. What's the percentage change?

Percentage Change = $\frac{1.25 - 1.00}{1.00} \times 100 = 25\%$

The candy bar's price increased by 25%.

📉 Team Score Drop

Your team scored 80 points in the first game and 60 points in the second game. What's the percentage change?

Percentage Change = $\frac{60 - 80}{80} \times 100 = -25\%$

Your team's score decreased by 25%.

➕ Another Example: Increase in Savings

You started with $50 in your savings account, and now you have $65. Calculate the percentage increase.

Percentage Change = $\frac{65 - 50}{50} \times 100 = 30\%$

Your savings increased by 30%.

🤔 Negative vs. Positive Change

• 📈 If the percentage change is positive, it means there was an increase.
• 📉 If the percentage change is negative, it means there was a decrease.

📝 Practice Quiz

1. A plant grew from 10 cm to 15 cm. What's the percentage change in height?
2. The price of a video game dropped from $60 to $45. What's the percentage change in price?
3. A recipe called for 2 cups of flour, but you only used 1.5 cups. What's the percentage change in the amount of flour used?
4. The number of students in a class increased from 20 to 24. Calculate the percentage increase.
5. A store sold 50 items on Monday and 40 items on Tuesday. What's the percentage change in sales?
6. A runner's time decreased from 25 minutes to 20 minutes. Calculate the percentage change in time.
7. The temperature increased from 20°C to 28°C. Find the percentage change in temperature.

✅ Percentage Change: Answers

1. 50% increase
2. 25% decrease
3. 25% decrease
4. 20% increase
5. 20% decrease
6. 20% decrease
7. 40% increase

⭐ Conclusion

Percentage change is a powerful tool for understanding how things change over time. Whether it's tracking prices, scores, or even the growth of a plant, mastering this concept will help you make sense of the world around you!