Suppose that y varies directly with x and inversely with z, and y = 18 when x = 15 and z = 5. Write the equation that models the relationship. Then find y when x = 21 and z = 7

Question

anonymous · Answer

$$y=C \times \frac{x}{z}$$Now use your initial conditions to find C, and then use that C to find the second y point.

anonymous · Answer

huh?

anonymous · Answer

Since y varies directly with x, as x gets bigger so does y.  As x gets smaller, so does y.  That is why in the equation I wrote, I multiplied C by x.

The same reason has me divide C by z.  Since as z gets smaller y gets bigger and as z gets bigger y gets smaller, we know that we must be dividing something by z.

So since when x=15 and z =5, y=18, I can say$$y=C \times \frac{x}{z}$$$$18=C \times \frac{15}{5}= C \times 3$$$$C=6$$So I can say$$y=6 \times \frac{x}{z}$$Now all you have to do is plug in the new values for x and z.

anonymous · Answer

would it be t = 6x/z; 18   or   t = 6z/x; 2

anonymous · Answer

I've basically already given you the answer.

anonymous · Answer

oh. thanks!!