Identify Percent Increase or Decrease
Identifying percent increase or decrease is a Grade 7 percent skill in Big Ideas Math, Course 2. A percent change measures how much a quantity increases or decreases relative to its original value. The formula is: percent change = (amount of change ÷ original amount) × 100%. If the new value is greater, it is a percent increase; if smaller, a percent decrease. For example, a price rising from $40 to $50 is a change of $10, giving (10 ÷ 40) × 100% = 25% increase. A drop from $80 to $60 gives (20 ÷ 80) × 100% = 25% decrease. Always divide by the original, not the new value.
Key Concepts
To determine the type of percent change: If new amount $ $ original amount, then percent increase If new amount $<$ original amount, then percent decrease If new amount $=$ original amount, then no change (0%).
Common Questions
What is the formula for percent change?
Percent change = (|new value − original value| ÷ original value) × 100%. If the new value is higher, it is a percent increase; if lower, a percent decrease.
How do you calculate the percent increase from $40 to $50?
Change = 50 − 40 = 10. Percent increase = (10 ÷ 40) × 100% = 25%.
How do you calculate the percent decrease from $80 to $60?
Change = 80 − 60 = 20. Percent decrease = (20 ÷ 80) × 100% = 25%.
What is the most common mistake when calculating percent change?
Dividing by the new value instead of the original value. Always use the original (starting) amount as the denominator.
How do you determine whether a change is an increase or decrease?
If the new value is greater than the original, it is an increase. If the new value is less than the original, it is a decrease.
Can percent change ever exceed 100%?
Yes—if a value more than doubles, the percent increase exceeds 100%. For example, a rise from $10 to $25 is a 150% increase.