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Finding a fraction of an amount is a useful skill you need for everyday, real-world math problems. For example, to find a discount price, or to determine a portion of something that you have (or a what portion you are missing), you need to know how to find the fraction of an amount. In these types of problems you will need to know how to multiply a fraction by a whole number, or how to create a fraction based on the information you are given. You might find that the most difficult part of these types of problems is determining what the problem is asking.

Method 1
Method 1 of 3:

Calculating an Amount

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  1. When a problem asks you what a fraction of a whole number is, the problem is one of multiplication, and you need to multiply the fraction and the whole number. Look for the keyword of . When you see of in a word problem, you need to multiply. [1]
    • For example, if the problem asks, “What is of ," you need to set up .
  2. To do this, give it a denominator of 1. Remember, the denominator is the number underneath the fraction bar. [2]
    • For example, you would change to . So the new problem becomes .
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  3. Remember that the numerators are the numbers above the fraction bars.
    • For example, .
  4. Place this number under the product of the numerators.
    • For example, , so .
  5. To do this, divide the numerator by the denominator. This will give you your final answer as a whole number or in decimal form. If the result is not a whole number and you need the answer written in the form of a fraction, you should reduce the fraction by dividing the numerator and denominator by their greatest common factor. For complete instructions on how to reduce a fraction, read Reduce Fractions . https://www.bbc.co.uk/bitesize/topics/zsxhfg8/articles/z33csrd
    • For example, , so of .
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    Joseph Meyer

    Math Teacher
    Joseph Meyer is a High School Math Teacher based in Pittsburgh, Pennsylvania. He is an educator at City Charter High School, where he has been teaching for over 7 years. Joseph is also the founder of Sandbox Math, an online learning community dedicated to helping students succeed in Algebra. His site is set apart by its focus on fostering genuine comprehension through step-by-step understanding (instead of just getting the correct final answer), enabling learners to identify and overcome misunderstandings and confidently take on any test they face. He received his MA in Physics from Case Western Reserve University and his BA in Physics from Baldwin Wallace University.
    Joseph Meyer
    Math Teacher

    To simplify fractions, you can divide both the numerator and denominator by a common factor. This creates a new, easier-to-use fraction with smaller components, but it represents the same value. For instance, if you divide both the numerator and denominator of 6/12 by 2, you get 3/6, which is equal to 1/2.

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Method 2
Method 2 of 3:

Calculating a Fraction

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  1. When a problem asks you what fraction one whole number is of another whole number, you need to create a fraction and reduce it. Look for the key phrases “fraction of” or “out of.” [3]
    • For example, if the problem asks, “What fraction of is ,” you need to create a fraction from the two given whole numbers.
  2. The numerator is the fraction of the whole. Often this will be the smaller number, but not always, so read the problem carefully. The denominator is the “complete” number. Look for the key phrase “fraction of .” The variable will be the denominator.
    • For example, if the problem asks, “What fraction of is ,” you know that is the numerator, because this is the number that is a part, or fraction, of . So the fraction is .
  3. To do this, find the greatest factor that is common to the numerator and the denominator, then divide each by that factor. For complete instructions on how to reduce fractions, read Reduce Fractions .
    • For example, the greatest common factor of and is :
      , so the reduced numerator is .
      , so the reduced denominator is .
      So, is of .
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Method 3
Method 3 of 3:

Changing an Amount By a Fraction

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  1. If the problem is asking you to determine how much of something is left, or to decrease an amount, or to find a discount, you will first multiply to find the fractional amount, then subtract the fractional amount from the original whole number. If the problem is asking you to determine how much of something there is after an increase, you will first multiply to find the fractional amount, then add the fractional amount to the original whole number. [4]
    • For example, a problem might ask, “If you have , and you give of it away, how much money do you have left?” In this case, you will multiply, then subtract.
    EXPERT TIP

    Joseph Meyer

    Math Teacher
    Joseph Meyer is a High School Math Teacher based in Pittsburgh, Pennsylvania. He is an educator at City Charter High School, where he has been teaching for over 7 years. Joseph is also the founder of Sandbox Math, an online learning community dedicated to helping students succeed in Algebra. His site is set apart by its focus on fostering genuine comprehension through step-by-step understanding (instead of just getting the correct final answer), enabling learners to identify and overcome misunderstandings and confidently take on any test they face. He received his MA in Physics from Case Western Reserve University and his BA in Physics from Baldwin Wallace University.
    Joseph Meyer
    Math Teacher

    Think about fractions as portions of a whole. Imagine dividing objects like pizzas or cakes into equal parts. Visualizing fractions this way improves comprehension, compared to relying solely on memorization. This approach can be helpful when adding, subtracting, and comparing fractions.

  2. To do this, turn the whole number into a fraction by placing it over a denominator of .
    • For example, to find , you would change the problem to .
  3. This will give you your new numerator.
    • For example, .
  4. This will give you your new denominator. Rewrite the new fraction.
    • For example, . So the new fraction is .
  5. First divide the numerator by the denominator to see if the result is a whole number. If the result is not a whole number, you should reduce the fraction by dividing the numerator and denominator by their greatest common factor. For complete instructions on how to reduce a fraction, read Reduce Fractions .
    • For example, , so of . This is the fractional amount you are decreasing by.
  6. This will give you your final answer.
    • For example, . So, if you have , and you give of it away, you have left.
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  • Question
    How much rope do I use if I have 9 1/4 meters of rope and use 2/7?
    Community Answer
    This problem is essentially asking, "What is 2/7 of 9 1/4?" So, you will multiply the two fractions to get your answer. For instructions on how to multiply two fractions, you can read the following article:http://www.wikihow.com/Multiply-Mixed-Numbers
  • Question
    Nine trucks are equal in weight to six trucks and four sedans. What fraction of the weight of a truck is the weight of a sedan?
    Community Answer
    You can set up the equation like this: 9x = 6x + 4y, where x = the weight of a truck, and y = the weight of a sedan. Since they want to know what fraction of a truck's weight (x) equals the weight of a sedan (y), you need to solve for y. 9x = 6x + 4y 3x = 4y 3/4x = y. So, the weight of a sedan is 3/4 the weight of a truck.
  • Question
    What is 3 quarters of 40?
    Community Answer
    3 quarters is the same as 3/4. So this is a multiplication problem: 3/4 x 40 = 3/4 x 40/1 = 120/4 = 30
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      About This Article

      Article Summary X

      To work out a fraction of a whole number, turn the whole number into a fraction by giving it a denominator of 1. Next, multiply the numerators together and write down the answer. Then, multiply the denominators together and write that answer under the product of the numerators to create a new fraction. You can then simplify the fraction by dividing the numerator by the denominator to get your final answer! For tips on calculating a fraction, read on!

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