A certain pen has been designed so that true average writing lifetime under controlled conditions (involving the use of a writing machine) is at least 12 hours. A random sample of 18 pens is selected, the writing lifetime of each is determined, and a normal probability plot of the resulting data supports the use of a one-sample t test.
a) What hypotheses should be tested if the investigator believes a priori that the design specification has been satisfied?
b) What conclusion is appropriate if the hypotheses of part a are tested, t = 2.5, and α = 0.05?
c) What conclusion is appropriate if the hypotheses of part a are tested, t = 2, and α = 0.01?
d) What should be concluded if the hypotheses of part a are tested and t = 3.25?