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If x is jointly proportional to the cube of y and the fou...

If x is jointly proportional to the cube of y and the fourth power of z. In what ratio is x increased or decreased when y is halved and z is doubled?

A.

4:1 increase

B.

2:1 increase

C.

1:1 no change

D.

1:4 decrease

E.

3:4 decrease

Correct answer is B

xy3z4

x=ky3z4

If y is halved and z is doubled, we have

x=k(12y)3(2z)4

x=k(y38)(16z4)\)

x=2ky3z4