x²+y²=20(10y+x)-(10x+y)=189y-9x=18, y-x=2, y²+x²-2xy=4, 20-2xy=4, xy=8. x=8/y.y-8/y=2y²-2y-8=0, (y-4)(y+2)=0, y=4; y=-2(舍去). x=2原来的两位数24