20 percent of my class is boys. There are 30 boys in class. How many girls in my class

20 percent of my class is boys. There are 30 boys in class. How many girls in my class?

Let c be the number of people in class. Since 20% = 0.2, We're given:
0.2c = 30

Type this equation into our search engine, we get:
c = 150

Since the class is made up of boys and girls, we find the number of girls in the class by this equation:
Girls = 150 - 30
Girls = 120