Which of the following is directly addressed by the null hypothesis?

Which of the following is directly addressed by the null hypothesis?
 
  A) The population before treatment
  B) The population after treatment
  C) The sample before treatment
  D) The sample after treatment

Question 2

A linear regression equation has b = 3 and a = - 6. What is the predicted value of Y for X = 4?
 
  A)  = 6
  B)  = -21
  C)  = -2
  D) This cannot be determined without additional information.

Question 3

A researcher conducts a hypothesis test to evaluate the effect of a treatment that is expected to increase scores. The hypothesis test produces a z-score of z = 2.37. If the researcher is using a one-tailed test, what is the correct statistical decision?
 
  A) Reject the null hypothesis with  = .05 but not with  = .01.
  B) Reject the null hypothesis with either  = .05 or  = .01.
  C) Fail to reject the null hypothesis with either  = .05 or  = .01.
  D) This cannot be answered without additional information.

Question 4

The Pearson correlation between X1 and Y is r = 0.70. When a second variable, X2, is added to the regression equation, we obtain R2 = 0.64. How much variance for the Y scores is predicted by using only X1 as a predictor variable?
 
  A) 0.06 or 6
  B) 0.15 or 15
  C) 0.49 or 49
  D) 0.70 or 70