2.4×7.5×1.25＝3×0.8×7.5×1.25＝（3×7.5）×（1.25×0.8）＝22.5×1＝22.5
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如图
0.8x3x7.5x1.25=7.5x3=22.5
=3*7.5*(0.8*1.25)=3*7.5*1=22.5
原式2.4×1.25×7.5=3*7.5=22.5
