How to Reduce Fractions Using Prime Factorization

Use prime factorization to reduce fractions. Start with numbers only and then add variables (letters that represent any real number) to the mix. The beauty of using the prime factorization is that you can be sure that the fraction’s reduction possibilities are exhausted — you can be certain that you haven’t missed any factors that the numerator and denominator may have in common.

Use these steps to reduce the following fraction:

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  1. Find the prime factorization of the numerator.

    120 is 23 × 3 × 5

  2. Find the prime factorization of the denominator.

    165 is 3 × 5 × 11

  3. Next, write the fraction with the prime factorizations in it.

    image1.png
  4. Cross out the factors the numerator shares with the denominator to see what’s left — the reduced form.

    image2.png

Now, try reducing the following fraction

image3.png

  1. Find the prime factorization of the numerator.

    100 is 22 × 52

  2. Find the prime factorization of the denominator.

    243 is 35

  3. Write the fraction with the prime factorizations.

    image4.png

    Look at the prime factorizations. You can see that the numerator and denominator have nothing in common. The fraction can’t be reduced. The two numbers are relatively prime. The beauty of using the prime factorization is that you can be sure that the fraction’s reduction possibilities are exhausted — you haven’t missed anything. You can leave the fraction in this factored form or go back to the simpler 100/243. It depends on your preference.

Now try reducing the following fraction that includes variables:

image5.png

  1. Find the prime factorization of the numerator.

    48x3y2z = 24 × 3 × x3 × y2 × z

  2. Find the prime factorization of the denominator.

    84xy2z3 = 22 × 3 × 7 × x × y2 × z3

  3. Write the fraction with the prime factorization.

    image6.png
  4. Cross out the factors in common.

    image7.png

Comments (1)

  1. Posted by stephanie
    nexts time put it in 5th gread words ok ok

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