Question

几道预初数学题,1.x:y=4:7x:z=3:5x-2y+3z=30 2.x/3=y/4=z/5x-2y+3z=30

Answer 1

1.x:y=4:7——7x=4y——y=7/4x

x:z=3:5——5x=3z-----z=5/3x

代入x-2y+3z=30 得x-2*7/4x+3*5/3x=30得x= 12 y=21 z=20

2.x/3=y/4=z/5--------- y=4/3x z=5/3x

带入 x-2y+3z=30得 x=9 y=12 z=15