原式=0.53×10×2.1+0.53×79=0.53×21+0.53×79=0.53×(21+79)=0.53×100=53
0.53x10x2.1+0.53x79=0.53x(21+79)=53
5.3（2.1﹢7.9)
＝5.3×10
＝53
0.53乘79这两个数，各伸缩10倍，积不变，于是得“5.3×7.9”。
5.3×2.1+0.53×79
=5.3×2.1+5.3×7.9
=5.3×(2.1+7.9)
=5.3×10
=53
5.3×2.1+0.53×79
=0.53×21+0.53×79
=0.53×(21+79)
=0.53×100
=53
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