Expressing a Fraction as a Percentage and Vice Versa

Concept sheet | Mathematics

In some situations, it is useful to switch from a percentage to a fraction or vice versa. The following concept sheet outlines the methods used to perform these conversions.

Expressing a Fraction as a Percentage

It is possible to express a fraction as a percentage. Here are two methods that can be used.

Method 1

The following method is most efficient when the denominator of the starting fraction is a divisor or multiple of |100|. Simply find an equivalent fraction whose denominator is |100.|

Rule
  1. Determine the number by which to multiply or divide the denominator to obtain |100.|

  2. Multiply or divide the numerator and denominator of the fraction by this number.

  3. Write the numerator of the fraction obtained in step 2 and add the % symbol to the right of it.

Example

Express the fraction |\displaystyle \frac{6}{25}| as a percentage.

  1. Determine the number by which to multiply or divide the denominator to obtain |100|
    It is possible to multiply the denominator of the fraction by |\color{green}{4}| to obtain |100|.||25\times \color{green}{4}=100||

  2. Multiply or divide the numerator and denominator of the fraction by this  number.||\displaystyle \frac{6\times \color{green}{4}}{25\times \color{green}{4}}=\frac{24}{100}||

  3. Write the numerator of the fraction obtained in step 2 and add the % symbol  to the right of it
    The answer is then |24\ \%.|

The following example uses division instead of multiplication to obtain a denominator of |100.|

Example

Express the fraction |\dfrac{163}{200}| as a percentage.

  1. Determine the number by which to multiply or divide the denominator to obtain |100|
    It is possible to divide the denominator of the fraction by |\color{green}{2}| to obtain |100|.||200\div \color{green}{2}=100||

  2. Multiply or divide the numerator and denominator of the fraction by this number ||\displaystyle \frac{163\div \color{green}{2}}{200\div \color{green}{2}}=\frac{81{.}5}{100}||

  3. Write the numerator of the fraction obtained in step 2 and add the % symbol to the right of it
    The answer is then |81{.}5\ \%.|

Method 2

This method is a little more complex than the first one but more versatile.

Rule
  1. Divide the numerator by the denominator.

  2. Multiply the quotient by |100.| 

  3. Add the % symbol to the right of the result.

Example

Write the fraction |\dfrac{5}{8}| as a percentage.

  1. Divide the numerator by the denominator

Image
  1. Multiply the quotient by |100| ||0{.}625\times 100=62{.}5||

  2. Add the % symbol to the right of the result
    |\dfrac{5}{8}| equals |62{.}5\ \%.|

Expressing a Percentage as a Fraction

Just as a percentage can be expressed as a fraction whose denominator is |100|, it is possible to convert a percentage to a fraction using the following method.

Rule
  1. Express the percentage as a fraction whose denominator is |100.| 

  2. If the numerator is not a whole number, convert it into a whole number by multiplying the numerator and the denominator by an appropriate power of |10|.

​Number of digits after the decimal

Power of |10|

​|1|

​|10|

​|2|

​|100|

​|3|

​|1\ 000|

​...

​...

  1.  If necessary, simplify the fraction to obtain an irreducible fraction.

There are two possible situations: either the percentage is a whole number, or the percentage is not a whole number. Here is an example of each situation.

Example

Express |28\ \%| in the form of an irreducible fraction.

  1.  Express the percentage as a fraction whose denominator is |100|||\dfrac{28}{100}||

  2. If the numerator is not a whole number, convert it into a whole number by multiplying the numerator and the denominator by an appropriate power of |10|
    Since the numerator is a whole number, we can go directly to step 3.

  3. If necessary, simplify the fraction to obtain an irreducible fraction ||\dfrac{28\color{green}{\div 4}}{100\color{green}{\div 4}}=\dfrac{7}{25}||

    |28\ \%| is equivalent to the irreducible fraction |\dfrac{7}{25}.|

Here is an example where the numerator is not a whole number.

Example

Express |72{.}4\ \%| in the form of an irreducible fraction.

  1. Express the percentage as a fraction whose denominator is |100| ||72{.}4\ \%=\displaystyle \frac{72{.}4}{100}||

  2. If the numerator is not a whole number, convert it into a whole number by multiplying the numerator and the denominator by an appropriate power of |10|
    Since the numerator has a number after the decimal point, we will have to multiply the numerator and the denominator by |10.| ||\dfrac{72{.}4\color{green}{\times 10}}{100\color{green}{\times 10}}=\dfrac{724}{1\ 000}||

  3. If necessary, simplify the fraction to obtain an irreducible fraction
    Simplify the fraction.||\dfrac{724\color{green}{\div 4}}{1\ 000\color{green}{\div 4}}=\dfrac{181}{250}||
    |72{.}4\ \%| is equivalent to the irreducible fraction |\dfrac{181}{250}.|

Exercise

Exercise

Fraction to a Percentage and Vice Versa

Mathematics Secondary1-2