Question

In a survey, a group of students were asked their favorite sport. Eighteen students chose “other” sports. Then how many students participated?

Answer 1

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