69×27–27×18=27×(69–18)=27×51=27×(50+1)=27×50+27=1350+27=137749×69=(50–1)×(70–1)=3500–70–50–1=3500–121=3379
69*27-27*18=27*（69-18）=27（50+1）=1350+27=137749*69=（50-1）*69=3450-69=3381
