如题所述
解
=3.5*3/7+0.65*8/13-3.5*2/7-0.65*5/13
=3.5*(3/7-2/7)+0.65*(8/13-5/13)
=3.5*1/7+0.65*3/13
=0.5+0.15
=0.65
希望你能采纳