Question

If x+y/y =13, what is the value of y/x?

Answer 1

Okay, to solve this we can use cross multiplication:
x+y = 13y
12y = x
Knowing this, we can safely say that
y/x = y/12y
y/12y = 1/12
y/x = 1/12

Answer 2

$\dfrac{x+y}{y}=13\\\\\dfrac{x}{y}+\dfrac{y}{y}=13\\\\\dfrac{x}{y}+1=13\ \ \ |-1\\\\\dfrac{x}{y}=12\to\dfrac{y}{x}=\dfrac{1}{12}$