City X has a population 7 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?  Choose the correct choice from the following answers.
A) 1:8  B) 1:4  C) 2:1  D) 14:1  E) 18:1
x= 7y, y= 2*z   X : Y , Y : Z   7 : 1 , 2 : 1   14 : 2 , 2 : 1   So, X : Z = 14 : 1   (14:1)
<result>D</result>
City X has a population 7 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?