The variable Z is directly proportional to X. When X is 12, Z has the value 228. What is the value of Z when X = 18

Question

 The variable Z is directly proportional to X. When X is 3, Z has the value 57.

What is the value of Z when X = 8

Answer 1

Z=Xk

228=12k

k=228/12

k=19

Z=18*19

Z=342

 

57=3k

57/3=k

19=k again

 

Z=8*19

Z=152

 

Answer 2

Since Z is directly proportional to X, Z = kX, for some constant, k.

 

When X = 12, Z = 57.  So, 57 = 12k

 

                                          Therefore, k = 57/12 = 19/4

 

Z = (19/4)X

 

When X = 8, Z = (19/4)(8) = 38