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Math (SAT®)205Updated Aug 31, 20262 pages

How to Calculate Percentages: A Guide for SAT Math

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Percentages help us express parts of a whole using numbers out of 100, making comparisons easier. Whether you're calculating a tip, understanding a discount, or analyzing data, knowing how to work with percentages is an essential math skill you'll use throughout life.
Calculating percentages – page 1

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Calculating Percentages

Ever wonder how to figure out sale prices or tips at restaurants? Percentages are the key! A percentage simply represents a portion of a whole as a number out of 100, shown by the "%" symbol.

To convert a percentage to a decimal form, just divide by 100. For example, 35% becomes 0.35. This makes calculations much easier. When you need to find a percentage of a number (like calculating a 20% tip), multiply the number by the percentage as a decimal. So 20% of 150wouldbe0.20×150 would be 0.20 × 150 = $30.

Sometimes you need to figure out what percentage one number is of another. Simply divide the first number by the second, then multiply by 100. For instance, to find what percentage 40 is of 80: (40 ÷ 80) × 100 = 50%.

Quick Tip: When working with percentages, converting to decimals first (by dividing by 100) makes calculations much simpler!

Calculating percentages – page 2

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Problem Solving with Percentages

Percent change helps you understand how much something has increased or decreased over time. This is super useful for tracking things like grades, prices, or population growth.

To calculate percent change, use this formula: Percent Change = (New Value - Old Value)/Old Value × 100. If your answer is positive, it shows an increase; if negative, it shows a decrease. For example, if a stock price rises from 50to50 to 60, the percent change is 60−5060-50/50 × 100 = 20% increase.

When solving percentage problems, start by carefully reading the question to identify what you know and what you need to find. Choose the right formula based on whether you're finding a percentage of a number, calculating what percentage one number is of another, or determining percent change.

Pro Strategy: Always double-check your work by asking "Does my answer make sense?" For example, if something increases by 100%, it should be double the original amount.

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