35 girls and boys went walking. The ratio is 5 girls to every 2 boys. How many boys are there?
\(5x-\ girls\\\\ 2x-\ boys\\\\ 5x+2x=35\\\\ 7x=35\ \ \ | divide\ by\ 7\\\\ x=5\\\\ There\ are\ 10\ boys.\)
Set up a proportion:
In a sample of 5:2, you have 7 kids in all.
So the the ratio of boys to kids in a sample of 7 is 2:7.
So set up a proportion:
\(\frac{2}{7}\) = \(\frac{X}{35}\)
7x =70
X = 10
Therefore, 10 of the boys went walking.