选t统计量,t=(根号n)(xba-u)/s------t(n-1)n=4,xba=30.42,s=0.21,a=0.05可得u的1-a置信区间为【xba- t1-a/2 (n-1)s/（根n) ,xba+ t1-a/2 (n-1)s/（根n) ];查表可得t 0.975(3)=3.1824带入数据区间为【30.09,30.75】...