Ski class

The class consists of 30 boys and some girls. Ski training was attended by 28 boys and all the girls, which was 95% of all students. How many girls attend this class? How much percent is that?

Correct answer:

x =  10
p =  25 %

Step-by-step explanation:

$$\begin{gathered} r=95\%=\frac{95}{100}=\frac{19}{20}=0.95 \\ 28+x=r\cdot (30+x) \\ 28+x=0.95\cdot (30+x) \\ 0.05x=0.5 \\ x=\frac{0.5}{0.05}=10 \\ x=10 \end{gathered}$$

$p=\frac{x}{x+30}\cdot 100=\frac{10}{10+30}\cdot 100=25\%$

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