4. In a primary school, among the students who completed 6th grade, 58% are boys. Of all the sixth-graders, 13 girls and 12 boys completed the grade with excellent success. Among the students who did not complete with excellent success, 60% are boys. How many boys, and how many girls did not complete with excellent success?
Solution. If $x$ is the number of all sixth-graders, then $(x-25)$ sixth-graders did not finish with excellent success. From the condition of the problem, it follows that:

$$
60\%(x-25)=58\% x-12
$$

which means

$$
\frac{60}{100}(x-25)=\frac{58}{100} x-12
$$

That is,

$$
60 x-1500=58 x-1200
$$

from which it follows that $x=150$. Therefore, $150-25=125$ sixth-graders did not finish with excellent success, of which $\frac{60}{100} 125=75$ boys and $125-75=50$ girls.

## VII Grade