algebra
posted by Juliette .
Could someone show me how to solve this joint variation problems?
Y varies jointly as x and y and inversely as w. Write the appropriate combined variation equation and find z for the given values of x, y and w. z=15 when x equals three, y equals four, and w equals nine, x equals 1.5 y equals 20.5 and w equals 5.4 (I don't know how to do a variation that is both joint and inverse).
Z varies jointly as x and y and inversely as w.. Write the appropriate combined variation equation and find z for the given values of x, y and w. y equals 120 when x equals eight and z equals 20; x equals 54 and z equals seven. (same problem as the last one).
If x1, y1 and x2, y2 satisfy xy=k, then x1y1 equals x2y2. 3,y and 18,6 (I am confused how x1y1=x2y2, yet the y values are differing). How do you find x or y for this?)
~Thanks for your help, Juliette

z=k(xy)/w
20=k(120*8)/20 find k
On the second part, (after the semicolon), y is not mentioned.
x1y1=k=x2y2 because xy=k for any x,y.
3y=18*6 solve for y. 
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