I don't get the first problem of my homework. We learned three lessons today, the increase, decrease, and finding the base number. But i don't know which one I should use. Please help with this problem: There are 12 girls in Mr. Cooper's class. The girls make up 40% of the class. How many students are in the class?

girls = 0.4 * total

so
12 = 0.4 * total
so
total = 12 / 0.4

total = 30

check:

0.4 * 30 = 12 yes

To solve this problem, you need to find the total number of students in Mr. Cooper's class. Since you know that the girls make up 40% of the class, you can use this information to determine the total number of students.

Here's the step-by-step explanation of how to solve this problem:

1. Start by understanding what "40%" means. Percentages represent a portion of a whole, where 100% represents the entire thing. In this case, 40% represents the girls in the class.

2. Next, you need to determine the base number, which represents the total number of students in the class. Since you're looking for the total number of students, the base number is what you want to find.

3. Apply the concept of finding the base number. To find the base number, you need to divide the given quantity (number of girls, in this case) by the percentage (40%, in this case).

4. Set up the equation: Let "x" be the total number of students in the class. You can write the equation as follows: 12/x = 40/100. Here, 12 represents the number of girls (the given quantity), and x represents the base number (the unknown quantity you're looking for).

5. Solve the equation: Cross-multiply and solve for x. Multiply 12 by 100 to get 1200, and then divide that by 40 to get x, which is the total number of students in the class.

1,200 / 40 = x
x = 30

Therefore, there are 30 students in Mr. Cooper's class.