First you need to calculate how many student is good at math, and that is by knowing how many student forms the 72% of the class total number. This is by multiplying the total number of the students by the percentage that are good at math. [tex]25* \frac{72}{100} =18[/tex] So 18 students are good at math. So the rest, which are not good at math, are equal to; [tex]25-18=7[/tex] The answer is 7. Hope this helps!
