Step-by-step explanation:
Classroom A has n students.
Since Classroom B has 4 less students, they have (n - 4) students.
Also Classroom C has double the students in B, so they have 2(n - 4) students.
We have A + B + C = 40.
=> n + (n - 4) + 2(n - 4) = 40
=> n + n - 4 + 2n - 8 = 40
=> 4n - 12 = 40
=> 4n = 52, n = 13.
Hence there are 13 students in Classroom A.
