Whenever the mean of the distribution of differences equals zero, ...

[nenivikky]

Whenever the mean of the distribution of differences equals zero, then one
   can be fairly safe in concluding that
 
  a. the samples probably represent a single population
  b. the samples probably represent different populations
  c. there was absolutely no sampling error
  d. none of these, since the mean can never equal zero

Question 2

If the mean of the distribution of differences were to equal -6.00, this
   would indicate that
 
  a. the standard deviation of the distribution is a function of the range
  b. the samples probably represent different populations
  c. the samples were probably selected from a single population
  d. none of these, since the mean can never be negative

[miss_1456@hotmail.com]

Answer to Question 1

a

Answer to Question 2

b