If 80% of the questions represent 20 questions, we can use the following rule of three to find how many questions are 100% of the questions:
[tex]\begin{gathered} \text{percentage}\to\text{questions} \\ 80\text{\%}\to20 \\ 100\text{\%}\to x \end{gathered}[/tex]Now we can write the following equation and solve it for x:
[tex]\begin{gathered} \frac{80}{100}=\frac{20}{x} \\ 80\cdot x=20\cdot100 \\ x=\frac{20\cdot100}{80} \\ x=25 \end{gathered}[/tex]Therefore the exam has 25 questions.
