Suppose that X denotes the amount of rainfall in your hometown during a given month and Y denotes the number of children born in Los Angeles during the same month.

Which of the following statements best explains why X and Y are not independent?

A. The ratio of the amount of rainfall in inches to the number of children born is usually one.
B. The amount of rainfall may tell you something about the season and, since births are seasonal, it may also tell you something about the number of children born.C. The variance for the amount of rainfall in inches is equal to the variance of the number of children born.
D. The expected value of rainfall in inches is equal to the expected number of children born.

B. The amount of rainfall may tell you something about the season and, since births are seasonal, it may also tell you something about the number of children born.

Explanation:

X is the variable for amount of rainfall and Y denotes the number of children born in Las Vegas.

If there is no relationship between them (that is occurrence of one does not affect the other) then they are independent variables.

If however the occurrence of one influences the other then they are dependent variables.

So if amount of rainfall tells what season we are in, and births are seasonal then the variables are related. As one can be used to deduce when the other will occur.