To calculate a percentage of a specific number, you need to convert the percentage into a decimal format or a fraction. First, divide the percentage value by 100 (e.g., 20% becomes 0.20). Then, multiply this decimal by the number in question. For example, to find 20% of 500, you would calculate 500 multiplied by 0.20, which equals 100. This method works for any percentage, whether it is a tax rate, a discount, or a portion of a whole.

To determine what percentage one number (the part) represents of another number (the whole), you perform a simple division followed by multiplication. First, divide the "part" by the "total" (Part ÷ Total). This gives you a decimal. Then, multiply that result by 100 to convert it into a percentage. For example, to find out what percentage 50 is of 200, you divide 50 by 200 to get 0.25. Multiplying 0.25 by 100 gives you 25%. This establishes the proportional relationship between the two values.

Calculating the percentage change involves finding the difference between two values relative to the starting value. First, subtract the old value from the new value (New Value - Old Value). Then, divide this difference by the *Old Value* (not the new one). Finally, multiply by 100. The formula is: ((New - Old) / Old) * 100. If the result is positive, it represents a percentage increase. If the result is negative, it indicates a percentage decrease. This is crucial for tracking growth or decline over time.