18.the equation that describe y varies jointly as x and y = kxz then k is obtained by?
a. k= xyz
b. k= y/xz
c. k= z/ky
d. k= xy/z
19.if two variables x and y are so related that their product is constants then y is always equal to which equation?
a. Y=kx
b. y=xk
c. y=k/x
d. y=x
20.if a bariable z varies directly as a bariable x and inversely as another variable y then what kind of bariation it is?
a. Linear
b. Joint
c. Inverse
d. Combined​