effectiveness of a cleanup project on a lake. Prior to the

Question

# The following information pertains to a study of the effectiveness of a cleanup project on a lake. Prior to the

project initiation, 12 water samples were obtained at random from this lake at the 2 pm peak period, and the amount of dissolved oxygen (in ppm) was recorded. The lake cleanup project was then carried out. Six months after the cleanup, 12 water samples were again taken at the 2 pm peak period, **independently** of the first samples before the cleanup, and the amount of dissolved oxygen (in ppm) was again recorded.

Let µ1 and σ1 denote the mean and standard deviation of Population 1 (data **after** the cleanup), and let µ2 and σ2 denote the mean and standard deviation of Population 2 (data **before** the cleanup). Use the information from the detailed Minitab output shown below to answer this question.

The point estimate of µ2 – µ1 and the pooled estimate SP of the common standard deviation are respectively

**Minitab Output **

**Descriptive Statistics: Before, After**

Variable N N* Mean SE Mean StDev Minimum Q1 Median Q3

Statistics and Probability