Assignment:
The idling speed of 14 gasoline-powered generators is measured with and without an oil additive that is designed to lower friction. With the additive installed, the mean change in speed was 23 revolutions per minute (rpm), with a standard deviation of + 3.5 rpm. At the 0.05 level of significance, is the additive effective in increasing engine rpm?
Provide complete and step by step solution for the question and show calculations and use formulas.