The drying time of a type of paint under specified test conditions is known to be normally distributed with a mean value of 75 min and a stand ard deviation of 9 min. Chemists have proposed a new additive desinged to decrease average drying time. It is believed that drying times with this additive will remain normally distributed with o = 9. Because of the expense associated with the additive, evidence should strongly suggest an improvement in aver age dry- ing time before such a conclusion is adopted. Let u denote the true average drying time when the additive is used. The appropriate hypotheses are Ho :µ = 75 versus Ha : µ < 75.

In mathematics, everyone must have heard the term average in one place or other. Almost all types of calculation require taking out an average. In everyday life, the term is used for denoting a certain amount that can be said to be a typical quantity for…