Question

The value of y varies directly with x. If y is 31.5 when x is 9, what is the value of x when y is 49?

Answer 1

You have that y varies directly with x, it means tha you can write the relation between both variables as follow:

$y=kx$

where k is the constant of proportionality.

If y = 3.15 when x = 9, you can find the value of k, just as follow:

$k=\frac{y}{x}=\frac{3.15}{9}=0.35$

Then, the equation that relates y and x can be writen as follow:

$y=0.35x$

or

$x=\frac{y}{0.35}$

Now, you can find the value of x when y = 49, by replacing this value into the previous equation:

$x=\frac{49}{0.35}=140$

Hence, the value of x when y = 49 is x = 140