How do you calculate the percentage of a number?
Multiply the number by the percentage and divide by 100: result = (number × percent) / 100. Example: 15% of 80 = (80 × 15) / 100 = 12. Shortcut: move the decimal two places — 15% of 80 = 0.15 × 80 = 12. Another: 7.5% of 200 = 0.075 × 200 = 15.
How do you calculate what percent one number is of another?
Divide the part by the whole and multiply by 100: percent = (part / whole) × 100. Example: 45 is what % of 180? = (45/180) × 100 = 25%. Example: score 18 out of 24 = (18/24) × 100 = 75%. Reverse: find the whole when the part and percent are known.
How do you calculate percent change (increase or decrease)?
Formula: % change = ((new − old) / old) × 100. Positive = increase, negative = decrease. Example: price rises from $50 to $65 → (65−50)/50 × 100 = +30%. Example: salary cut from $3,000 to $2,700 → (2700−3000)/3000 × 100 = −10%.
What is the percentage difference between two numbers?
Percentage difference measures the relative gap between two values with no fixed reference: % diff = |A − B| / ((A + B) / 2) × 100. Example: comparing 90 and 110 → |90−110| / 100 × 100 = 20%. Unlike percent change, neither value is treated as the "original".
How do you reverse a percentage (find the original value before increase/decrease)?
Divide by the multiplier. After a 20% increase, price is $60 — what was the original? x × 1.20 = 60 → x = 60 / 1.20 = $50. After a 15% discount, price is $85 → x × 0.85 = 85 → x = $100. Never subtract the percentage directly — always divide by (1 ± rate).
How do you add or subtract a percentage from a number?
Add P%: multiply by (1 + P/100). Example: add 8% to £50 → 50 × 1.08 = £54. Subtract P%: multiply by (1 − P/100). Example: 10% discount on $80 → 80 × 0.90 = $72. Common uses: VAT, GST, tips, and discounts.
What are common real-world uses for a percentage calculator?
Common uses: shopping discounts (20% off $150 = $120), restaurant tips (15% of $64 = $9.60), tax calculations (VAT, GST, sales tax), pay raises (5% increase on $40,000 = $42,000), exam grades (72/90 = 80%), and investment returns (portfolio from $10,000 to $11,500 = +15%).
What is the difference between percentage points and percent change?
A percentage point is an absolute arithmetic difference between two percentages. Example: interest rate rises from 3% to 5% = 2 percentage points, but as percent change = (5−3)/3 × 100 = +66.7%. Confusing the two is a common error in financial reporting and news headlines.
