If x and y vary directly and x=2 when y =3 find x when y=39

Answer 1

Neenah, do you know the definition of “direct variation”? The general formula is

y = kx

or alternatively

y/x = k

So you first task is to discover k.

You know that y = 3 when x = 2, so fill those values in to discover k.

Then once you have a value, rewrite the first equation by filling in the value of k and the value of x, do the arithmetic and you’ll have the value of y.

Does this help?

Answer 2

Hi Neenah S.,

When x and y vary directly, it is when y is equal to some constant times x or y = c*x.

Since we are given an x and a y we can solve for c.

3 = c*2 or 3/2 = c and the equation becomes y = 3/2*x.

We can now solve for when y = 39:

39 = 3/2*x

(2/3)*39 = x

26 = x, the answer.

I hope this helps, Joe.

Answer 3

Just remember that the equation for a direct variation can always be written in the form y=kx

Given y=3 when x=2, 3 = k2 . So k = 3/2. Therefore, your equation is y = (3/2)x.

Then just plug in the 39 to solve for the x.

39 = (3/2)x

Divide 39 by 3/2.

x = 26