Unfortunately, arsenic occurs naturally in some ground watert. A mean arsenic level of u= 8.0 parts per billion (ppb) is considered safe for agricultural use. A well in Texas is used to water cotton crops. This well is tested on a regular basis for arsenic. A random sample of 41 tests gave a sample mean of x = 6.9 ppb arsenic, with s = 2.7 ppb. Does this information indicate that the mean level of arsenic in this well is less than 8 ppb? Use a = 0.01. (a) Wh: ir the nifi

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Unfortunately, arsenic occurs naturally in some ground watert. A mean arsenic level of u = 8.0 parts per billion (ppb) is considered
safe for agricultural use. A well in Texas is used to water cotton crops. This well is tested on a regular basis for arsenic. A random
sample of 41 tests gave a sample mean of x = 6.9 ppb arsenic, with s = 2.7 ppb. Does this information indicate that the mean level of
arsenic in this well is less than 8 ppb? Use a = 0.01.
(a) What is the level of significance?
0.01
State the null and alternate hypotheses.
= 8 ppb; H1: u # 8 ppb
O Ho: 4 > 8 ppb; H1: u = 8 ppb
O Ho: H = 8 ppb; H1: u > 8 ppb
O Ho: H < 8 ppb; H1: µ = 8 ppb
O Ho: 4 = 8 ppb; H1: µ < 8 ppb
(b) What sampling distribution will you use? Explain the rationale for your choice of sampling distribution.
The Student's t, since the sample size is large and o is unknown.
O The Student's t, since the sample size is large and o is known.
O The standard normal, since the sample size is large and o is known.
O The standard normal, since the sample size is large and o is unknown.
What is the value of the sample test statistic? (Round your answer to three decimal places.)
2.609
Transcribed Image Text:Unfortunately, arsenic occurs naturally in some ground watert. A mean arsenic level of u = 8.0 parts per billion (ppb) is considered safe for agricultural use. A well in Texas is used to water cotton crops. This well is tested on a regular basis for arsenic. A random sample of 41 tests gave a sample mean of x = 6.9 ppb arsenic, with s = 2.7 ppb. Does this information indicate that the mean level of arsenic in this well is less than 8 ppb? Use a = 0.01. (a) What is the level of significance? 0.01 State the null and alternate hypotheses. = 8 ppb; H1: u # 8 ppb O Ho: 4 > 8 ppb; H1: u = 8 ppb O Ho: H = 8 ppb; H1: u > 8 ppb O Ho: H < 8 ppb; H1: µ = 8 ppb O Ho: 4 = 8 ppb; H1: µ < 8 ppb (b) What sampling distribution will you use? Explain the rationale for your choice of sampling distribution. The Student's t, since the sample size is large and o is unknown. O The Student's t, since the sample size is large and o is known. O The standard normal, since the sample size is large and o is known. O The standard normal, since the sample size is large and o is unknown. What is the value of the sample test statistic? (Round your answer to three decimal places.) 2.609
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