Math test

Obelix filled out a mathematical test in which he answered 25 questions. For every correct answer, he received 5 points. For each wrong answer, he had 3 points deducted. Obelix gained 36% of all points in the test. How many questions did he solve correctly?

Correct answer:

n =  15

Step-by-step explanation:

$$\begin{gathered} p=36\%=\frac{36}{100}=\frac{9}{25}=0.36 \\ t=25 \\ 5n-3(t-n)=p\cdot t\cdot 5 \\ 5n-3(25-n)=0.36\cdot 25\cdot 5 \\ 5\cdot n-3\cdot (25-n)=0.36\cdot 25\cdot 5 \\ 8n=120 \\ n=\frac{120}{8}=15 \\ n=15 \end{gathered}$$

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