If y=7.5 when x=0.5, find y when x=-3My algebra one teacher is horrible! I never understand anything she is saying! Please explain in simple terms!

Expert Answers
pohnpei397 eNotes educator| Certified Educator

Okay, the first thing you need to do is figure out what the relationship is between x and y.  Here's how you do that:

First, write a direct-variation formula

y = kx  where k is the constant of variation.  Plug in the y and x values that you know.

7.5 = .5k

To find for k, multiply both sides by 2 and you get k = 15

By that, we know that y is 15 times bigger than x.

So now all you have to do is plug your other value for X into that equation (y = kx).  Remember that we know that k = 15

So that gives us y = 15*-.3

And when you do the math, you get

y = -4.5


ndnordic eNotes educator| Certified Educator

In general you can set up probems like this as a ratio where y1/x1 = y2/x2.  In your problem, y1 is 7.5, x1 is 0.5 and x2 is -3.  y2 is what you want to find. You then have 7.5/0.5 = y/-0.3 and you can solve for y.  If you use this ratio methodyou can solve for any of the four variables by entering the known values for the other three.

Wiggin42 | Student

If y=7.5 when x=0.5, find y when x=-0.3

You can set up proportions: 

`(.5)/(7.5) = (-0.3)/(y)`

`.5y = -2.25`

`y = -2.25 /.5`

`y = -4.5`


` `

talleighchris | Student

oh no!!!! It's actually -0.3, not -3!