49×1.4=(50-1)×1.4=50×1.4-1×1.4=70-1.4=68.6
49x1.4=(50-1)x1.4=50x1.4-1.4=70-1.4=68.6
(50一1)X1.4=50X1.4一1X1.4=70一1.4=68.96
=49X(1+0.4)=49+19.6=68.6