x-(1/5+1/5)x-39=39 x-1/4x-2/5x=112 x-1/6x-1/3x-12=20
问题描述：
x-(1/5+1/5)x-39=39 x-1/4x-2/5x=112 x-1/6x-1/3x-12=20
答
x-(1/5+1/5)x-39=39 x-2/5x=39+393/5x=78x=78÷3/5x=130x-1/4x-2/5x=112 (1-1/4-2/5)x=1127/20x=112x=112÷7/20x=320x-1/6x-1/3x-12=20(1-1/6-1/3)x=20+121/2x=32x=32÷1/2x=64