设X～N(1．5，4)，求：
(1)P(X＜3．5)；
(2)P(X<-4)；
(3)P(X＞2)；
(4)P(|X|＜3)．
μ=1.5，σ2=4，σ=2． (1)P(x＜3.5)=φ[(3.5-1.5)/2]=φ(1)=0.8413． (2)P(x＜-4)=φ[(-4-1.5)/2]=φ(-2.75) =1-φ(2.75)=0.0030． (3)P(X＞2)=1-P(X≤2)=1-φ[(2-1.5)/2] =1-φ(0.25)=1-0.5987=0.4013． (4)P(|X|＜3)=P(-3＜X＜3) =φ[(3-1.5)/2]-φ[(-3-1.5)/2] =φ(0.75)-φ(-2.25) =φ(0.75)-1+φ(2.25) =0.7612．
