Question

Help!!!! I have done multiple questions of this type an keep getting it wrong somehow. I’ve tried plugging the number into the formula and I’m doing something wrong..

so here it is:
Y varies inversely with the cube of x. If y= 375 when x=1/5, find y when x=1/4

Answer 1

y = 192.

Explanation:

y = k/x^3 where k is the constant of variation.

When x = 1/5 y = 375, so:

375 = k / (1/5)^3

375 = k / 1 /125

125k = 375

k = 3.

So the equation of variation is y = 3/x^3

and when x = 1/4:

y = 3 / (1/4)^3

y = 3 * 64

= 192.

Answer 2

y = k/cuberoot(x)

Gotta find k first.

375 = k/cuberoot(1/5)

375•cuberoot(1/5) = k

We now know k.

Let x = 1/4

Let k = 375•cuberoot(1/5)

y = [375•cuberoot(1/5)] ÷ cuberoot(1/4)

To find y, plug right side into calculator.