If 30% of the students in a class made a B and there were 12 Bs how many students were in the class?

1. Let the total number of students in the class be denoted by x.
2. According to the problem, 30% of the students made a B, and this equals 12 students.
3. Set up the equation:

0.30 \times x = 12

4. To find x, divide both sides of the equation by 0.30:

x = \frac{12}{0.30}

5. Simplify the right side:

x = \frac{12}{0.30} = 40

6. Therefore, the total number of students in the class is \boxed{40} .

Answer: 40 students.