So, we're going to add some number of boys to the class. We don't know how many, but we can assign a variable to it anyway. Let's call that unknown number x. After adding the boys, there will be 18 + x boys in the class, and a total of 48 + x students. We want the

ratio of boys to girls to be five to three. That means for every five boys, there needs to be three girls. Suppose the class had only 8 students and it was in this ratio. How many boys would there be? Now suppose the class had 16 students and was in this ratio. How many boys would there be then? How did you figure out these answers? What does that suggest about the

proportion of the class that must be boys after adding x boys? Using that knowledge, can you set up an

equation to model the fact that 18 + x must be (that proportion) of 48 + x students?

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