Percentages, Percentage Increase & Decrease Practice Problems
A percentage represents parts per 100. Master benchmark percentage calculations (10%, 25%, 50%), decimal multipliers for percent increase/decrease (sales tax and discounts), and calculating relative percentage change from original base values.
🧠 Core Problem-Solving Strategies
⚡ The Decimal Multiplier Method
To increase by 20%, multiply by 1.20. To decrease by 15%, multiply by (1 − 0.15) = 0.85.
📊 Percentage Change Formula
% Change = ((New Value − Original Value) / Original Value) × 100%. Always divide by the ORIGINAL amount!
🖐️ 10% & 1% Mental Building Blocks
Find 10% by shifting decimal 1 place left. Double for 20%, halve for 5%.
❓ Frequently Asked Questions
Why must you divide by the original value when calculating percentage change?
Because percentage change measures growth or decay relative to where you started (the baseline).
What is the fastest way to calculate 15% tip in your head?
Find 10% (shift decimal left by 1), take half of that to get 5%, and add them together.
Continue Learning & Practicing
Reinforce your understanding with printable worksheets, step-by-step guides, calculators, and speed games: