[20又1/3-18又1/5+16又1/7+14又2/3-12又4/5+10又6/7】x【9-25/31】
=[(20又1/3+14又2/3)-(12又4/5+18又1/5)+(16又1/7+10又6/7)】x【9-25/31】
=[35-31+27]×[9-25/31]
=31×9-31×25/31
=279-25
=254