Question

The ratio of girls to all students in a class is 3/5.What is the ratio of boys to all students in the class? If there are 15 girls in the class. How many students are in the class?

Answer 1

So we are being asked about the ratio of boys to all students and the only information we have is the ratio of girls to all students. Since students can either be boys or girls then we know that the sum of both ratios must be 1. Then, if we use B to label the ratio of boys we have:

`\begin{gathered} 1=B+(3)/(5) \\ 1-(3)/(5)=B \\ B=(2)/(5) \end{gathered}`

So the ratio of boys to all students is 2/5.

Next, we need to find the number of students in the class. We know that 15 are girls and since 3/5 of the total number of students are girls this means that:

`(3)/(5)\cdot N=15`

Where N is the number of students. Now we just need to find N using this equation:

`\begin{gathered} (3)/(5)\cdot N=15 \\ 3\cdot N=15\cdot5 \\ 3N=75 \\ N=(75)/(3)=25 \end{gathered}`

So there are 25 students in the class.