\BeginKnitrBlock{exercise}\iffalse{-91-68-101-102-105-110-105-110-103-32-115-116-97-116-105-115-116-105-99-97-108-32-104-121-112-111-116-104-101-115-101-115-93-}\fi{}<div class="exercise"><span class="exercise" id="exr:unnamed-chunk-88"><strong>(\#exr:unnamed-chunk-88)  \iffalse (Defining statistical hypotheses) \fi{} </strong></span>Write down the null hypothesis $H_0$ and the alternative hypothesis $H_1$ we wish to test given we want to perform a two--sided test! Hint: use the two (unknown) site mean values $\mu_1$ and $\mu_2$.</div>\EndKnitrBlock{exercise}