方差的置信度为98%的置信区间--->α=1-0.98=0.02,α/2=0.01,1-α/2=0.99置信区间=[ns^2/χ^20.01(19),ns^2/χ^20.99(19)]=[320/36.191 320/7.633]=[8.842 41.9]
