Math 2 questions~~

1) x+y+z=100.................(I)
10x+0.5y+0.1z=100........(II)
10*(I)-(II)
10x+10y+10z-(10x+0.5y+0.1z)=10*100-100
9.5y+9.9z=900
95y+99z=9000
(y,z)=(27,65),(-72,160)...
(x,y,z)=(8,27,65),(12,-72,160)...

2) x+y+z=100...............(I)
10x+y+0.5z=100...........(II)
10*(I)-(II)
10x+10y+10z-(10x+y+0.5z)=10*100-100
9y+9.5z=900
18y+19z=1800
(y,z)=(5,90),(24,72)...
(x,y,z)=(5,5,90),(4,24,72)...