The mean weekly sales of a four-wheeler were 50 units per agency in 20 agencies. After an advertising campaign, the mean weekly sales increased to 55…

The mean weekly sales of a four-wheeler were $\displaystyle 50$ units per agency in $\displaystyle 20$ agencies. After an advertising campaign, the mean weekly sales increased to $\displaystyle 55$ units per agency with standard deviation of $\displaystyle 10$ units. Test whether the advertising campaign was successful. (Use $\displaystyle \mathrm{t}_{0.005}=1.729$ for $\displaystyle 19$ d.f.)