Definitions Complement rule: P(A^(C))=P(not A)=1-P(A) Addition rule for disjoint or mutually exclusive events: P(A ∪ B)=P(A or B)=P(A)+P(B) Solution The probability P(0<= z<= 0.55) is given in the row with z=0.5 and in the column with .05 of the normal probability table in the appendix: P(0<= z<= 0.55)=0.2088 The probability P(0<= z<= 2.16) is given in the row with z=2.1 and in the column with .06 of the normal probability table in the appendix. The standard normal distribution is symmetric about 0: P(-2.16<= z<= 0)=P(0<= z<= 2.16)=0.4772 Add the corresponding probabilities: P(-2.16<= z<= 0.55)=P(0<= z<= 0.55)+P(-2.16<= z<= 0) =0.2088+0.4846=0.6934