42×41/43=(43-1)×42/43=43×42/43-1×42/43=42-42/43=41又1/431/8×1/12+1/3×1/8=1/8×(1/12+1/3)=1/8×5/12=5/964/11×10+4/11=4/11×(10+1)=4/11×11=4