Suppose y varies directly with x, and y=20 when x= -5. Find x when y=24.

Question

anonymous · Answer

Can you help me? I'm stuck

whpalmer4 · Answer

$$y = kx$$ is the form for direct variation of $y$ with $x$

we know a pair of values for $x,y$, so use that to find the value of $k$

anonymous · Answer

Alright. So it would be 20=k*-5?

whpalmer4 · Answer

yes!

anonymous · Answer

Okay. So what do I do now? I find K?

whpalmer4 · Answer

yes, what value of $k$ will make that work?

once you know $k$, you plug your new value of $y$ or $x$ into the equation and find the missing value

anonymous · Answer

So K=-4. Now what?

freckles · Answer

y=-4x is the equation you have

remember your question ask you to find x when y is 24.

freckles · Answer

so solve for x when y is 24...

whpalmer4 · Answer

exactly.
$$y=-4x$$$$24=-4x$$$$x=$$

anonymous · Answer

I'm not understanding this part.

anonymous · Answer

Does x=-6?

whpalmer4 · Answer

it does!

anonymous · Answer

That's it?

whpalmer4 · Answer

seems almost too easy, doesn't it? :-)

anonymous · Answer

Yes. Thank you! :D

whpalmer4 · Answer

You knew that the two were related by direct variation, so that established the $y = kx$ formula.  You knew a pair of values, so that established the value of $k$.  Now you can find the corresponding value to any value of $x$ or $y$.

anonymous · Answer

Okay. Thank you. This has helped a lot.

whpalmer4 · Answer

Glad to hear it!