1,设第一块地为x公顷,则第二块为100-x公顷,根据题意:
2x/5+3(100-x)/5=50
2x+3(100-x)=250
x=50
100-x=50
两块地都是50公顷
2,4X-6Y=8 (1)
4X-3Y=17 (2)
(2)-(1)得:3Y=9,Y=3,代回(1)得:4X-18=8,4X=26,X=13/2
3,2X-3Y=5 (1)
3X+9Y=12 (2)
(1)x 3+(2)得:9X=27,X=3,代回(1)得:6-3Y=5,Y=1/3
4,3X-2Y=8 (1)
4X-3Y=5 (2)
(1)x3-(2)x2 得:9x-8x=24-10,X=14,代回(1)得:42-2Y=8,Y=17
5.X-Y=3 (1)
X+Y=7 (2)
(1)+(2)得:2X=10,x=5
(2)-(1)得:2Y=4,Y=2