How to find 50 percent of a number

Find a percentage or work out the percentage given numbers and percent values. Use percent formulas to figure out percentages and unknowns in equations. Add or subtract a percentage from a number or solve the equations.

How to Calculate Percentages

There are many formulas for percentage problems. You can think of the most basic as X/Y = P x 100. The formulas below are all mathematical variations of this formula.

Let's explore the three basic percentage problems. X and Y are numbers and P is the percentage:

1. Find P percent of X
2. Find what percent of X is Y
3. Find X if P percent of it is Y

Read on to learn more about how to figure percentages.

1. How to calculate percentage of a number. Use the percentage formula: P% * X = Y

Example: What is 10% of 150?

• Convert the problem to an equation using the percentage formula: P% * X = Y
• P is 10%, X is 150, so the equation is 10% * 150 = Y
• Convert 10% to a decimal by removing the percent sign and dividing by 100: 10/100 = 0.10
• Substitute 0.10 for 10% in the equation: 10% * 150 = Y becomes 0.10 * 150 = Y
• Do the math: 0.10 * 150 = 15
• Y = 15
• So 10% of 150 is 15
• Double check your answer with the original question: What is 10% of 150? Multiply 0.10 * 150 = 15

2. How to find what percent of X is Y. Use the percentage formula: Y/X = P%

Example: What percent of 60 is 12?

• Convert the problem to an equation using the percentage formula: Y/X = P%
• X is 60, Y is 12, so the equation is 12/60 = P%
• Do the math: 12/60 = 0.20
• Important! The result will always be in decimal form, not percentage form. You need to multiply the result by 100 to get the percentage.
• Converting 0.20 to a percent: 0.20 * 100 = 20%
• So 20% of 60 is 12.
• Double check your answer with the original question: What percent of 60 is 12? 12/60 = 0.20, and multiplying by 100 to get percentage, 0.20 * 100 = 20%

3. How to find X if P percent of it is Y. Use the percentage formula Y/P% = X

Example: 25 is 20% of what number?

• Convert the problem to an equation using the percentage formula: Y/P% = X
• Y is 25, P% is 20, so the equation is 25/20% = X
• Convert the percentage to a decimal by dividing by 100.
• Converting 20% to a decimal: 20/100 = 0.20
• Substitute 0.20 for 20% in the equation: 25/0.20 = X
• Do the math: 25/0.20 = X
• X = 125
• So 25 is 20% of 125
• Double check your answer with the original question: 25 is 20% of what number? 25/0.20 = 125

Remember: How to convert a percentage to a decimal

• Remove the percentage sign and divide by 100
• 15.6% = 15.6/100 = 0.156

Remember: How to convert a decimal to a percentage

• Multiply by 100 and add a percentage sign
• 0.876 = 0.876 * 100 = 87.6%

Percentage Problems

There are nine variations on the three basic problems involving percentages. See if you can match your problem to one of the samples below. The problem formats match the input fields in the calculator above. Formulas and examples are included.

• Written as an equation: Y = P% * X
• The 'what' is Y that we want to solve for
• Remember to first convert percentage to decimal, dividing by 100
• Solution: Solve for Y using the percentage formula
  Y = P% * X

• Written using the percentage formula: Y = 10% * 25
• First convert percentage to a decimal 10/100 = 0.1
• Y = 0.1 * 25 = 2.5
• So 10% of 25 is 2.5

• Written as an equation: Y = P% ? X
• The 'what' is P% that we want to solve for
• Divide both sides by X to get P% on one side of the equation
• Y ÷ X = (P% ? X) ÷ X becomes Y ÷ X = P%, which is the same as P% = Y ÷ X
• Solution: Solve for P% using the percentage formula
  P% = Y ÷ X

• Written using the formula: P% = 12 ÷ 40
• P% = 12 ÷ 40 = 0.3
• Convert the decimal to percent
• P% = 0.3 × 100 = 30%
• So 12 is 30% of 40

• Written as an equation: Y = P% * X
• The 'what' is X that we want to solve for
• Divide both sides by P% to get X on one side of the equation
• Y ÷ P% = (P% × X) ÷ P% becomes Y ÷ P% = X, which is the same as X = Y ÷ P%
• Solution: Solve for X using the percentage formula
  X = Y ÷ P%

• Writen using the formula: X = 9 ÷ 60%
• Convert percent to decimal
• 60% ÷ 100 = 0.6
• X = 9 ÷ 0.6
• X = 15
• So 9 is 60% of 15

• Written as an equation: P% * X = Y
• The 'what' is P% that we want to solve for
• Divide both sides by X to get P% on one side of the equation
• (P% * X) ÷ X = Y ÷ X becomes P% = Y ÷ X
• Solution: Solve for P% using the percentage formula
  P% = Y ÷ X

• Written using the formula: P% = 6 ÷ 27
• 6 ÷ 27 = 0.2222
• Convert decimal to percent
• P% = 0.2222 × 100
• P% = 22.22%
• So 22.22% of 27 is 6

• Written as an equation: P% × X = Y
• The 'what' is X that we want to solve for
• Divide both sides by P% to get X on one side of the equation
• (P% × X) ÷ P% = Y ÷ P% becomes X = Y ÷ P%
• Solution: Solve for X using the percentage formula
  X = Y ÷ P%

• Written using the formula: X = 7 ÷ 20%
• Convert the percent to a decimal
• 20% ÷ 100 = 0.2
• X = 7 ÷ 0.2
• X = 35
• So 20% of 35 is 7.

• Written as an equation: P% * X = Y
• The 'what' is Y that we want to solve for
• Solution: Solve for Y using the percentage formula
  Y = P% * X

• Written using the formula: 5% * 29 = Y
• Convert the percent to a decimal
• 5% ÷ 100 = 0.05
• Y = 0.05 * 29
• Y = 1.45
• So 5% of 29 is 1.45

• Written as an equation: Y / X = P%
• The 'what' is X that we want to solve for
• Multiply both sides by X to get X out of the denominator
• (Y / X) * X = P% * X becomes Y = P% * X
• Divide both sides by P% so that X is on one side of the equation
• Y ÷ P% = (P% * X) ÷ P% becomes Y ÷ P% = X
• Solution: Solve for X using the percentage formula
  X = Y ÷ P%

• Written using the formula: X = 4 ÷ 12%
• Solve for X: X = Y ÷ P%
• Convert the percent to a decimal
• 12% ÷ 100 = 0.12
• X = 4 ÷ 0.12
• X = 33.3333
• 4 of 33.3333 is 12%

• Written as an equation: Y / X = P%
• The 'what' is Y that we want to solve for
• Multiply both sides by X to get Y on one side of the equation
• (Y ÷ X) * X = P% * X becomes Y = P% * X
• Solution: Solve for Y using the percentage formula
  Y = P% * X

• Written using the formula: Y = 11% * 25
• Convert the percent to a decimal
• 11% ÷ 100 = 0.11
• Y = 0.11 * 25
• Y = 2.75
• So 2.75 of 25 is 11%

• Written as an equation: Y / X = P%
• The 'what' is P% that we want to solve for
• Solution: Solve for P% using the percentage formula
  P% = Y / X

• Written using the formula: P% = Y / X
• 9 ÷ 13 = P%
• 9 ÷ 13 = 0.6923
• Convert decimal to percent by multiplying by 100
• 0.6923 * 100 = 69.23%
• 9 ÷ 13 = 69.23%
• So 9 of 13 is 69.23%

Related Calculators

Find the change in percentage as an increase or decrease using the Percentage Change Calculator.

Solve decimal to percentage conversions with our Decimal to Percent Calculator.

Convert from percentage to decimals with the Percent to Decimal Calculator.

If you need to convert between fractions and percents see our Fraction to Percent Calculator, or our Percent to Fraction Calculator.

References

Weisstein, Eric W. "Percent." From MathWorld -- A Wolfram Web Resource.

Learn the basics of how to calculate percentages of quantities in this easy lesson! To find a percentage of any number, use this generic guideline of TRANSLATION: Change the percentage into a decimal, and the word "of" into multiplication. See many examples below.

The concepts and ideas of this lesson are also explained in this video:

1. "Translate" the expressions into multiplication by a decimal. Calculate.

2. "Translate" the other way: write the multiplications as expressions of "percentage of the number".

    a. 17% of $4500

    b. 67% of 27 m

4. Use mental math to find percentages of these quantities.

5. a. A lake has a 30-km long shoreline. 6% of it is sandy beach. What percentage of the shoreline is not sandy beach?

6. Twenty percent of a university’s 4,000 students have a scholarship.

    a. What percent of the students do not have a scholarship?

    b. How many students have a scholarship?

8. Identify the errors that Gladys made. Then find the correct answer.

Find 80% of 50.

    Gladys’s solution:
    80 × 50 = 4,000

9. Find the expressions with the same value as 20% of $620.

11. The table below shows Andy’s usage of time in one day.

      a. Calculate the time he spent in each activity.
    Round the minutes to the nearest minute.

      b. Label the sections in the circle graph with the name of each activity.
 

Andy’s Usage of Time

Percent – free lesson

Percentage of a number using mental math – free lesson

How to calculate percentages – free lesson

Basics of percent of change – free lesson

Interactive fraction, decimal and percentage tool This tool shows you a fraction visually (bar or pie) and converts the fraction into a percentage and decimal. You can show or hide the equivalent percentage and decimal.

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This lesson is taken from Maria Miller's book Math Mammoth Percent, and posted at www.HomeschoolMath.net with permission from the author. Copyright © Maria Miller.