City X has a population 3 times as great as the population of City Y, which has a population twice as great as the population of City Z. What is the ratio of the population of City X to the population of City Z?  Pick one
A) 1:8
B) 1:4
C) 2:1
D) 6:1
E) 8:1
x= 3y, y= 2*z   X : Y , Y : Z   3 : 1 , 2 : 1   6 : 2 , 2 : 1   So, X : Z = 6 : 1   (6:1)
<result>D</result>
City X has a population 3 times as great as the population of City Y, which has a population twice as great as the population of City Z. What is the ratio of the population of City X to the population of City Z?