18 students are 100%-37,5%-40%=22,5%
So we know that 18 students equal to 22.5. And we are looking for the anwser what 100% of students is.
SO:
x students - 100%
(22 + 1/2)x =18×100
(22 + 1/2) can be represented as just 25.5
-//- = 1800
we need to divide bot sides by 25.5
x = 1800 / 25.5
... x = 80
