10.81 A student organization uses the proceeds from a particular soft-drink dispensing machine to finance its activities. The price per can had been $0.75 for a long time, and the average daily revenue during that period was $75.00. The price was recently increased to $1.00 per can. A random sample of n 5 20 days after the price increase yielded a sample mean daily revenue and sample standard deviation of $70.00 and $4.20, respectively.

Does this information suggest that the mean daily revenue has decreased from its value before the price increase? Test the appropriate hypotheses using a 5 .05.