(a) If A and B are disjoint, P(A) = 0.4 and P(B) = 0.5, then P(A OR B) = 0.9.

(b) If the variance for a data set is zero, then all the observations in this data set must be identical.

(c) There may be more than one mode in a data set.

(d) A 90% confidence interval is wider than a 95% confidence interval of the same parameter.

(e) In a right-tailed test, the value of the test statistic is 2. The test statistic follows a distribution with the distribution curve shown below. If we know the shaded area is 0.03, then we have sufficient evidence to reject the null hypothesis at 0.05 level of significance.