This is a paired comparison question:
The answer is:
However, this is my thought of using a t test on difference of population means
$t=\frac{583.125 - 415 - 0}{\sqrt{\frac{262.5900866^2}{8}+\frac{261.5721698^2}{8}}}$
$t= 1.2829$
$df=13.99978881$
critital value $t_{0.05}(df=14)$= 1.76131
$1.2829 < 1.76131$
therefore no difference between the mean daily sales from the two stores. Why am I getting a different conclusion? Is it reasonable to think about it this way?