Question

Given that y and x are directly proportional and y=3 when x=6, find the value of y when x=18.

Answer 1

Answer:

y = 9

Step-by-step explanation:

If x and y are directly proportional, then the quotient y : x is constant.

We have:

x = 6 and y = 3

x = 18 and y = ?

We have the equation:

$3:6=y:18\\\\\dfrac{3}{6}=\dfrac{y}{18}\qquad\text{cross multiply}\\\\6y=(3)(18)\\\\6y=54\qquad\text{divide both sides by 6}\\\\\dfrac{6\!\!\!\!\diagup y}{6\!\!\!\!\diagup}=\dfrac{54}{6}\\\\y=9$