To find out how many students attend the school, we can use the information that 840 students represent 75% of the total student population.
Let \( x \) be the total number of students at the school. We can set up the equation:
\[ 0.75x = 840 \]
To solve for \( x \), we divide both sides by 0.75:
\[ x = \frac{840}{0.75} \]
Calculating the right side:
\[ x = 1120 \]
So, the total number of students who attend that school is 1,120 students.