Problem 1. In a school, 58% of the total number of students are boys. How many were boys and how many were girls if the number of boys and girls differs by 72? How many students were there in total in that school?
Solution. Let $x$ denote the total number of students in this school. From the condition of the problem, we have $\frac{58-42}{100} x=72$, and from this $x=450$. This means there were a total of 450 students in the school, and this $\frac{58}{100} \cdot 450=261$ boys and $450-261=189$ girls.