设随机变量X服从正态分布N(3，4)，求：
(1)P(2﹤X﹤3)；
(2)P(-4≤X≤10)；
(3)P(∣X∣﹥2)；
(4)P(X﹥3)．
(1)P(2﹤X﹤3)=Φ[(3-3)/2]-Φ[(2-3)/2] =Φ(0)-Φ(-0.5) =Φ(0)-1+Φ(0.5) =0．191． (2)P(-4≤X≤10)=Φ[(10-3)/2]-Φ[(-4-3)/2] =Φ(3.5)-Φ(-3．5) =Φ(3．5)-1+Φ(3．5) =2Φ(3．5)-1 =0．9996 (3)P(∣X∣﹥2)=1-P(∣X∣≤2) =1-{Φ[(2-3)/2]-Φ[(-2-3)/2]} =1-Φ(-0．5)+Φ(-2．5) =1-1+Φ(0.5)+1-Φ(2．5) =1+Φ(0．5)-Φ(2．5) =0．697． (4)P(X﹥3)=1-P(x﹤3) =1-Φ[(3-3)/2] =1-Φ(0) =0．5．
