21.已知XXX服从正态分布N(2,σ2)N(2,\sigma ^{2})N(2,σ2),且P(1⩽X⩽2)=0.4P(1\leqslant X\leqslant 2)=0.4P(1⩽X⩽2)=0.4,则P(X>3)=P(X>3)=P(X>3)=[ 0.1 ].