Assume that y varies inversely as x. If y = -6 when x = -2, find y when x = 5.

Question

johnweldon1993 · Answer

Varying inversely would mean you use the equation

$$y = \frac{ k }{ x }$$

first...we want to solve for 'k' to use later....so you have
y = -6
x = -2

plug those into that equation and solve for 'k'...what do you get?

anonymous · Answer

-2=k/-6

johnweldon1993 · Answer

Well you actually switched the 'x' and 'y' it should be

-6 = k/-2

but close..

so now..solve for 'k' by multiplying both sides of the equation by -2..what does 'k' equal?

anonymous · Answer

k=12 ?

johnweldon1993 · Answer

right....that is what we get for 'k'

Now...we have a second part of the question...solving for y when x = 5

to do this we use that same equation

$$y = \frac{ k }{ x }$$

you now know....k = 12 and x = 5 so plug those in..and solve for y...

anonymous · Answer

what is 12/5 ?

johnweldon1993 · Answer

12 / 5 equates to 2.4

so y = 2.4 when x = 5

anonymous · Answer

thanks! can you help with this: Assume that y varies inversely with x. If y = 8.8 when x = 2.4, find x when y = 2.1. Round to the nearest tenth.

johnweldon1993 · Answer

This would be the same thing...

use the equation

$$y = \frac{ k }{ x }$$

input your 'y' and 'x' to solve for 'k' first....then use that 'k' and your given 'y' value to solve for 'x'

anonymous · Answer

ok thanks for the equation. that will help tons! :D

johnweldon1993 · Answer

No problem...

Remember that varying inversely 

$$y = \frac{ k }{ x }$$

if it says it varies directly you would use

$$y = k x$$

hope that helps!