6.6 The Department of Natural Resources (DNR) received a complaint from recreational fishermen that a community was releasing sewage into the river where they fished. These types of releases lower the level of dissolved oxygen in the river and hence cause damage to the fish residing in the river. An inspector from the DNR designs a study to investigate the fishermen's claim. Fifteen water samples are selected at locations on the river upstream from the community and fifteen samples are selected downstream from the community. The dissolved oxygen readings in parts per million (ppm) are given in the following:

Upstream 5.2 4.8 5.1 5.0 4.9 4.8 5.0 4.7 4.7 5.0 4.6 5.2 5.0 4.9 4.7

Downstream 3.2 3.4 3.7 3.9 3.6 3.8 3.9 3.6 4.1 3.3 4.5 3.7 3.9 3.8 3.7

(a) Calculate mean, standard deviation, and standard error for upstream and downstream, respectively.

(b) Compute the standard error of (Y1-Y2" style="box-sizing: border-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); border: 0px; max-width: 100%; height: auto; display: inline; vertical-align: middle; line-height: inherit; max-height: 31.25rem;"> ) for these data.

(c) Use these data to construct a 90% confidence interval for the population difference in the means of the dissolved oxygen readings.