The level of dissolved oxygen (DO) in a stream or river is an important indicator of the water's ability to support aquatic life. A researcher measures the DO level at 15 randomly chosen locations along a stream. Here are the results in milligrams per liter (mg/l): 4.53, 5.04, 3.29,5.23,4.13,5.50, 4.83, 4.40,5.42,6.38,4.01,4.66, 2.87,5.73,5.55 A dissolved oxygen level below 5 mg/1 puts aquatic life at risk.

(a) A frequency histogram of the data is given below. Explain why it is most appropriate to apply t procedures with this sample
(b) Do we have convincing evidence at the 0.05 significance level that aquatic life in this stream is at risk?
c) Given your conclusions of part (b), which kind of error - Type 1 vs Type II - could you have made? Explain what this mistake would mean in context?