How do you write $80\%$ as a fraction?

Hint: This is a problem in which the student has to bring the percentage into a fraction in its simplest form. This can be treated as a problem in fraction in which the first step would be to convert a percentage into a fraction by dividing it by $100$. And then the student can bring both the numbers in their simplest form.

Complete Step by Step Solution:
The first step is to convert the given percentage into the form of a fraction
 $80\%=\dfrac{80}{100}$
The second step is to bring numerator and denominator in terms of its prime factors.
$\dfrac{80}{100}=\dfrac{4\times 4\times 5}{5\times 5\times 4}$
From the above step, we can see that the fraction has the greatest common multiple $25$. Striking off the common multiple we get the fraction in its simplest form.
$\dfrac{80}{100}=\dfrac{4}{5}$

Thus, the simplest form of the fraction is $\dfrac{4}{5}$.

Note:
The only important step in this sum is to first bring the percentage into a fraction and then in terms of its prime factors. Sometimes when the complicated sum like $30\%\times \dfrac{3}{20}\times \dfrac{4}{40}$, it is advisable that the student first converts all the terms into the form of a fraction and then cancel out common terms after which, he/she should reduce the remaining terms to its the prime factors.