解方程组：X/30+Y/20+(75-X-Y)/40=2.5 X/30+(75-X-Y)/20+Y/40=2.8
问题描述：
解方程组：X/30+Y/20+(75-X-Y)/40=2.5 X/30+(75-X-Y)/20+Y/40=2.8
答
X/30+Y/20+(75-X-Y)/40=2.5 4X+6Y-3X-3Y =X+3Y=2.5*120-75*3
X/30+(75-X-Y)/20+Y/40=2.8 4X+3Y-6X-6Y =-2X-3Y=2.8*120-75*6
-X=5.3*120-75*9 X=75*9-5.3*120=3(3*75-53*4)=3*13=39
3Y=2.5*120-75*3 Y=2.5*40-75=25