# In a class of 42 students, the number of boys is 2/5 of the girls. How do you find the number boys and girls in the class?

Dec 27, 2016

We turn that into equations:

#### Explanation:

(1) $B + G = 42$

(2) $B = \frac{2}{5} \times G$

Replacing $B$ by (2) we get:

$\frac{2}{5} \times G + G = 1 \frac{2}{5} \times G = 42$

Turning $1 \frac{2}{5}$ into a non-mixed fraction:

$\frac{7}{5} \times G = 42 \to$ multiply by 5, divide by 7:

$G = 42 \times \frac{5}{7} = \frac{6 \times \cancel{7} \times 5}{\cancel{7}} = 30$

$B = \frac{2}{5} \times 30 = \frac{2}{\cancel{5}} \times \cancel{5} \times 6 = 12$

And these add up to 42.