设红气球为X,黄气球为Y,蓝气球为Z
X+Y+Z=240 X+Y+Z=240 X=40
X=(Y+Z)*20% → 5X-Y-Z=0 → Y=120
Z:(X+Y)=1：2 X+Y-2Z=0 Z=80
红气球为40个,黄汽球为120个,蓝气球为80个