=6.24
解:依题意,简便计算方法如下7.8×0.9-7.8×0.1=7.8×(0.9-0.1)=7.8×0.8=(8-0.2)×0.8=8×0.8-0.2×0.8=6.4-0.16=6.24
7.8x0.9-7.8x0.1=7.8x(0.9-0.1)=7.8x0.8=6.24
7.8×0.9 - 7.8×0.1= 7.8×1 - 7.8×0.2= 7.8 - 1.56= 6.24