than 7.0 ppb. A random sample of 40 tests gave a sample mean of = x_bar = 7.5 ppb arsenic, with s = 1.9 ppb.  a. DF = 40, t-test statistic = 1.664, p-value = 0.0520 b. z-test statistic = 1.664, p-value = 0.0481 c. z-test statistic = 0.163, p-value = 0.4353 d. DF = 39, t-test statistic = 1.664, p-value = 0.0520

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Arsenic (chemical element) occurs naturally in some ground water. A mean arsenic level of μ = 7.0 per billion is (ppb) consider safe for agricultural use. A well in Texas is used to water cotton crops. This well is tested on a regular basis for arsenic. Test the claim that the arsenic in the ground water is more than 7.0 ppb.
A random sample of 40 tests gave a sample mean of = x_bar = 7.5 ppb arsenic, with s = 1.9 ppb. 

a. DF = 40, t-test statistic = 1.664, p-value = 0.0520
b. z-test statistic = 1.664, p-value = 0.0481
c. z-test statistic = 0.163, p-value = 0.4353
d. DF = 39, t-test statistic = 1.664, p-value = 0.0520
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