原式=5/31×(-2/9)×(-2又1/15)×(-4又1/2) 有三个负因数,积为负,带分数化成假分数
=-(5/31×2/9×31/15×9/2)
=-(5/31×31/15)×(2/9×9/2)
=-1/3×1
=-1/3