Boys and girls

If the ratio of male and female teachers is 2/5 and the proportion of male and female students is the same, how many are girls if there are 42 boys?

Correct answer:

g =  30

Step-by-step explanation:

$$\begin{gathered} b:g=2:5 \\ b+g=42 \\ g\cdot \frac{2}{5}+g=42 \\ g=\frac{42}{1+\frac{2}{5}}=30 \end{gathered}$$

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