A soap manufacturing company was distributing a particular brand of a soap through a large number of retail shops. Before a heavy advertisement…

A soap manufacturing company was distributing a particular brand of a soap through a large number of retail shops. Before a heavy advertisement campaign, the mean sales per week per shop was $\displaystyle 140$ dozen. After the campaign, a sample of $\displaystyle 26$ shops was taken and mean sales was found to be $\displaystyle 147$ dozen with standard deviation 16. Can you consider the advertisement campaign effective? [Given $\displaystyle \mathrm{t}_{25}(0.05)=2.06$]