Calculate Girls in Class: 70% of 40 Students are Boys

To solve this problem, we'll follow these steps:

• Step 1: Calculate the number of boys in the class using the percentage given.
• Step 2: Subtract the number of boys from the total number of students to determine the number of girls.

Now, let's work through each step:
Step 1: Calculate the number of boys.
The percentage of boys in the class is given as 70%. Thus, we calculate the number of boys as follows:

$\text{Number of boys} = \frac{70}{100} \times 40 = 28$

Step 2: Calculate the number of girls.
Since there are 40 students in total, the number of girls can be found by subtracting the number of boys from the total number of students:

$\text{Number of girls} = 40 - 28 = 12$

Therefore, the solution to the problem is $12$.