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05-11-2006, 01:08 AM
Suppose X varies directly with Y and Z and inversely with W, and X=3 when Y=2, Z=6, and W=16. Find X when Y=7, Z=20, and W=5.


I know how to do joint variation, but not so sure how to do directly in this kind if situation. Please help, much help would be appreciated

steve_b
05-11-2006, 09:26 AM
Suppose X varies directly with Y and Z and inversely with W, and X=3 when Y=2, Z=6, and W=16. Find X when Y=7, Z=20, and W=5.

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First, write an equation which shows the relationships, with "k" as the "constant of variation":

x = k y z / w

Next, substitute for the values given:

3 = k * 2 * 6 / 16

Solve this for K

k = 3 * 16 / (2 * 6) = 4

Your equation can now be written:

x = 4 y z / w

Now substitute y=7, z=20, and w=5 to get x.

Hope that helps...

Steve

05-11-2006, 04:31 PM
I did what you told me and I got 112. Am I correct?

steve_b
05-11-2006, 04:39 PM
Yes, that's what I get too. Be sure to try more problems like this one so you get more practice.

Steve

05-11-2006, 04:43 PM
Thank you very much!