A ratio can be written in three different ways: 3 to 4, 3:4, and 3/4
What does this mean? It means that for every group of 7 students (3+4) there are 3 boys and 4 girls. And how many groups do we have? We have:
245/7= 35 We have 35 groups, and we just said that each group has 3 boys and 4 girls:
35*3= 105 boys
35*4= 140 girls
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Total: 245 students
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Here's how to set up an equation:
Let's call the number of girls x. Since the total is 245 students, 245-x= boys:
Set up the equation by writing the number of students in the ratio as a fraction:
3/4= (245-x)/x Cross multiply:
3x= 4(245-x) Multiply on right:
3x= 980-4x Add 4x on both sides:
7x= 980 Divide both sides by 7:
x= 140 this is how many girls there are. And:
245-140= 105= boys
