87×0.38-8.7+72×0.87
=87x(0.38-0.1+0.72)
=87x1
=87
87×0.38-8.7+72×0.87
=0.87×38-0.87×10+0.87×72
=0.87×(38-10+72)
=0.87×100
=87
87×0.38-8.7+72×0.87
=87×0.38-87×0.1+0.72×87
=87×（0.38-0.1+0.72）
=87×1
=87
8.7x（3.8-1+7.2）
=8.7x10=87
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