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

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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