怎么解这方程Y/(X+Y)=40% Y/(X+Y+5)=30%
问题描述：
怎么解这方程Y/(X+Y)=40% Y/(X+Y+5)=30%
答
Y/(X+Y)=40%
Y=0.4X+0.4Y
0.6Y=0.4X
Y=2X/3
代入Y/(X+Y+5)=30%
Y=0.3X+0.3Y+1.5
2X/3=0.3X+0.2X+1.5
X/6=1.5
所以X=9
Y=2X/3=6