Y= (X- 1)/2

E(Y)= E((X- 1)/2)=( 1/2)E(X)- 1/2 =- 1/2

D(Y)= D((X- 1)/2)=( 1/4)D(X)= 1/4

Y=(X- 1)/2 ~N(- 1/2， 1/4)

Mathematical expectation of (X- 1)/2 =-1/2.