Listed below are time intervals (min) between eruptions of a geyser. Assume that the "recent" times are within the past few years, the "past" times are from around 20 years ago, and that the two samples are independent simple random samples selected from normally distributed populations. Do not assume that the population standard deviations are equal. Does it appear that the mean time interval has changed? Is the conclusion affected by whether the significance level is 0.10 or 0.01?

Recent

78

90

90

79

56

101

61

86

70

87

82

82

56

82

75

101

61

Past

90

88

93

94

63

85

86

92

88

91

91

91

Let 1 be the recent times and let 2 be the past times. What are the null and alternative hypotheses?

A.

H0: 12

H1: 1=2

B.

H0: 1<2

H1: 1=2

C.

H0: 1=2

H1: 12

D.

H0: 1=2

H1: 1>2