Question

Out of 30 students are surveyed 17 have a dog based on these results predict how many of the 300 students in the school have a dog

Answer 1

 17 / 30  =  x / 300

cross multiply 

30x = 5,100

divide by 30

x = 170


or 


$\frac{17}{30} * 10 = \frac{170}{300}$

if it is simpler.

Answer 2

$From\ proportion:\\ 30\ students\ 17\ dogs\\ 300\ students\ x\ dogs\\\\Cross\ multiplication\\ 30x=300*17\\ 30x=5100\ \ \ | divide\ by\ 30\\ x=170\\\\ There\ will\ be\ 170\ dogs\ for\ 300\ students.$