Final answer:
The percentage of girls in the class is 40%, calculated by setting up the fraction of girls to total students (12/30) and then multiplying by 100.
Step-by-step explanation:
To calculate the percentage of girls in a class of 30 students, where 12 are girls, we would set up a fraction of girls to total students and then convert that fraction to a percentage. The fraction representing the girls is ⅖, since there are 12 girls out of 30 students. To find the percentage, we multiply this fraction by 100:
⅖ × 100 = 40%
Therefore, the percentage of girls in the class is 40%.