Q&A for How to Divide and Multiply Fractions

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  • Question
    Can I simplify fractions before multiplying/dividing them?
    Grace Imson, MA
    Math Instructor, City College of San Francisco
    Grace Imson is a math teacher with over 40 years of teaching experience. Grace is currently a math instructor at the City College of San Francisco and was previously in the Math Department at Saint Louis University. She has taught math at the elementary, middle, high school, and college levels. She has an MA in Education, specializing in Administration and Supervision from Saint Louis University.
    Math Instructor, City College of San Francisco
    Expert Answer
    Yes, and it will make things easier if you do, especially if you're working with really big numbers.
  • Question
    Can you clarify Step 1, please?
    Community Answer
    Step 1 says to multiply the numerators--that means multiply the top number in both fractions. For example, if you want to multiply 2/3 (two thirds) and 1/2 (one half), I would start by multiplying 2 and 1 together.
  • Question
    How do I divide negative fractions?
    Community Answer
    The same way you would positive fractions. If both fractions have the same sign your answer will be positive regardless of whether they are both negative or both positive. But if your fractions have different signs, you will get a negative answer.
  • Question
    How do I divide and multiple negative fractions?
    Donagan
    Top Answerer
    Same as with positive fractions, except the sign of the answer may be affected. If one of the fractions is negative, the answer will be negative. If both of the fractions are negative, the answer will be positive.
  • Question
    What are the steps to multiplying fraction with common and different denominators?
    Community Answer
    Multiply the numerator by the other numerator, and multiply the same number with each of the denominators. You then can divide to the smallest whole values for each.
  • Question
    How do I know when to reduce?
    Donagan
    Top Answerer
    Reduce whenever you can exactly divide a whole number into both the numerator and denominator. It's easiest to recognize when you can divide a small integer (like 2, 3 or 5) into both the numerator and denominator.
  • Question
    How do I multiply mixed fractions that are in brackets?
    Community Answer
    First change each mixed fraction into an improper fraction. For example, change 1 1/2 to 3/2. Then follow the steps given to multiply the improper fractions.
  • Question
    How do you add and subtract fractions?
    Community Answer
    First, make the denominator of the fractions equivalent. Then add the numerators or subtract them.
  • Question
    How do I multiply and divide negative fractions?
    Donagan
    Top Answerer
    Ignore signs while multiplying/dividing. Once you have the final number, count the negative signs among the original fractions. If there is an odd number of negative signs, the answer has a negative sign. If there is zero or an even number of negative signs, the answer has a positive sign.
  • Question
    What does "of" mean when using fractions?
    Community Answer
    In word problems, the word "of" typically indicates multiplication. Three-fifths of two hundred women means (3/5)x200 or 120 women.
  • Question
    What does it mean to multiply and divide fractions?
    Community Answer
    It's just like normal multiplication and division. You see what the value you would get from multiplying the numbers, or from dividing them.
  • Question
    How do I divide mixed numbers and fractions?
    Community Answer
    You need to convert the mixed number into an improper fraction and then divide the fractions normally.
  • Question
    If the numerator is higher than the denominator, do I have to turn it into a mixed fraction?
    Donagan
    Top Answerer
    It's not required, but it is customary to do so.
  • Question
    How do I divide a fraction by a whole number?
    Donagan
    Top Answerer
    There are two ways to do this: (1) Divide the numerator by the whole number if it will divide evenly. (2) Multiply the denominator by the whole number, then reduce the fraction if possible.
  • Question
    How do I divide 39/195 by common factors?
    Community Answer
    39 divided by 13 = 3. 195 divided by 13 = 15. Therefore, the answer is 3/15 or simplified: 1/5
  • Question
    Do I need to take the lowest common multiple of the fraction while multiplying and dividing it?
    Community Answer
    No, you need to take the greatest common factor (GCF) to simplify it. To multiply, you multiply them regularly: the top first, and then the bottom. To divide, you flip one of the fractions and divide it that way, and then you can simplify it by the (GCF).
  • Question
    What is the value of 9/4 x 11/10 in lowest terms?
    Community Answer
    9/4 x 11/10 = 99/40. this is already in its simplest form, so just convert it to a mixed number or leave it this way.
  • Question
    How do I multiply mixed numbers?
    Community Answer
    To multiply mixed numbers, you need to turn your mixed number into an improper fraction. Then, you can multiply that to get your answer. wikiHow's article on multiplying mixed numbers might be helpful to you too.
  • Question
    How do I multiply whole numbers and fractions?
    Community Answer
    Add a 1 to the whole number as a denominator. Then, multiply your number by your fraction.
  • Question
    How do I multiply mixed fractions?
    Community Answer
    Change the mixed fraction into a improper fraction. Then do the step as shown. For example, if you had 3 4/5, change it to 19/5. Then do the steps.
  • Question
    What happens if I am dividing three fractions?
    Community Answer
    You can't divide three fractions. The process of division involves dividing one number (or fraction) into another.
  • Question
    A bag of candy weighs 8 1/3 pounds. One serving is 1/3 pound. How many servings are in the bag?
    Donagan
    Top Answerer
    The question is: how many one-thirds (1/3) are there in 8 1/3? To find out, divide 8 1/3 by 1/3. 8 1/3 is 25/3. 25/3 ÷ 1/3 = (25/3)(3/1) = 75/3 = 25. There are 25 servings in the bag.
  • Question
    What is the easiest way to reduce fractions?
    Donagan
    Top Answerer
    Look for the largest number that will divide exactly into both the numerator and the denominator. Perform those divisions to reduce the fraction as far as possible. For example, to reduce 28/189, we must recognize that 28 is exactly divisible by 2, 4 and 7, and 189 is exactly divisible by 3, 7 and 9. So the largest integer that is exactly divisible into both the numerator and the denominator is 7. Perform those two divisions, and we're left with 4/27, the fully reduced fraction.
  • Question
    What is "cross cancelling?"
    Donagan
    Top Answerer
    It's a way of making multiplication of fractions a little easier. It involves cancelling a number (or a factor) in one numerator and the same number (or factor) in another denominator. Here's an example: An easy way to multiply 4/7 by 21/44 is first to factor the numerators and denominators where possible. 4/7 is (2)(2) / 7, and 21/44 is (3)(7) / (2)(2)(11). Now cancel both 2's in the first numerator and both 2's in the second denominator, and cancel the 7 in the first denominator and the 7 in the second numerator. The cancellations leave these fractions to be multiplied: (1/1)(3/11), with an easy product of 3/11.
  • Question
    Can you explain what gcf means?
    Community Answer
    The GCF, or Greatest Common factor, is the largest number that two numbers can both be divided by.
  • Question
    Why do we have to reverse the second fraction and multiply instead of dividing?
    Community Answer
    Are you thinking of dividing numerators and dividing denominators analogous to the multiplication rule? Like (3/10) / (1/5) = (3/1) / (10/5) = 3/2. That's also a perfectly valid technique (you can check that it equals (3/10)*(5/1)). The only reason it isn't usually taught is that, unless the numbers work out as nicely as in this example, you'll get a fraction of fractions. You'll then be expected to simplify that in which case you won't save any time over the usual method. So it's a good trick when it works out nicely, but the advantage of converting to a multiplication problem is that it limits how messy the simplification can get.
  • Question
    What is two and three-fourths divided by two thirds?
    Donagan
    Top Answerer
    2¾ / 2/3 = 11/4 / 2/3 = (11/4)(3/2) = 33/8 = 4 1/8.
  • Question
    How do I multiply improper fractions?
    Donagan
    Top Answerer
    Multiply them the way you multiply any fractions: numerator times numerator, and denominator times denominator. The product will be an improper fraction, which you should reduce and then, if you prefer, change to a mixed number.
  • Question
    Do you multiply denominators that are the same?
    Custard 008
    Community Answer
    Regardless of what the denominators are, the method is the same. Just multiply the two denominators to get your new one.
  • Question
    When you have to multiply and divide three fractions in the same problem (like 4/3 divided by 20/3 times 11/9,) what do you do first?
    Donagan
    Top Answerer
    Work left to right: first divide4/3 by 20/3. Then multiply that quotient by 11/9.
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