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A student answers 80% of the questions on a math exam correctly. If she answers 20 questions correctly, how many questions are on the exam?

Sagot :

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.