15.6×13.1-15.6-15.6×2
=15.6×（13.1-1-2）
=15.6×10.1
=15.6×10+15.6×0.1
=156+1.56
=157.56
515.6×13.1-15.6-15.6x2=(500+15.6)x13.1-15.6x3=500x13.1+15.6x13.1-15.6x3=6550+15.6x(10+3+0.1)一15.6x3=6550+15.6x10+15.6x3+15.6x0.1-15.6x3=6550+156+1.56=6607.56
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