设甲桶有X升,乙桶有Y升,丙桶有Z升,则有
1)甲1/2X 乙1/4X+Y 丙1/4X+Z
2)甲1/2X+(1/4X+Y)/4 即是9/16X+1/4Y 乙(1/4X+Y)/2即是1/8X+1/4Y 丙1/4X+Z+(1/4X+Y)/4 即是 5/16X+1/4Y+Z
3)甲9/16X+1/4Y+(5/16X+1/4Y+Z)/4即是41/64X+5/16Y+1/4Z
乙1/8X+1/4Y+(5/16X+1/4Y+Z)/4即是13/64X+9/16Y+1/4Z
丙(5/16X+1/4Y+Z)/2即是5/32X+1/8Y+1/2Z
组成方程组
41/64X+5/16Y+1/4Z=8
13/64X+9/16Y+1/4Z=8
5/32X+1/8Y+1/2Z=8
解得X=4,Y=7,Z=13