(* Ross Cap. 8 n. 17 *)

x={26.,24.,20.,25.,27.,25.,28.,30.,26.,33.};
n=Length[x]
m=Mean[x]
s2=Variance[x]
s=Sqrt[s2]

t=(m-30.)/s*Sqrt[n]

(* Ross Cap. 8 n. 18 *)

x={237.,242.,244.,262.,225.,218.,242.,248.,243.,234.,236.,228.,232.,230.,254.,220.,232.,240.};
n=Length[x]
m=Mean[x]
s2=Variance[x]
s=Sqrt[s2]

t=(m-240.)/s*Sqrt[n]