Differentiate between Z-test at t –test. Industrial wastes, sewage dumped into our rivers, streams absorb oxygen and thereby reduce the amount of dissolved oxygen available for fish and other forms of aquatic life. One state agency requires a minimum of 8 parts per million (ppm) of dissolved oxygen in order for the oxygen content to be sufficient to support aquatic life. Eight water specimens taken from a river at a specification location during the low-water season gave the readings 4.5, 5.1, 4.8, 4.9, 5.1, 4.9, 5.0 and 4.7 ppm of dissolved oxygen. Do the data provide sufficient evidence to indicate that the dissolved oxygen content is less than 5ppm? Use 5% level of significance.