15.6×13.1－15.6－15.6×2.1
=15.6×（13.1-1-2.1）
=15.6×10
=156
6.4×0.25＋3.6÷4
=6.4×1/4+3.6×1/4
=1/4×（6.4+3.6）
=1/4×10
=5/2
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15.6×13.1－15.6－15.6×2.1
=15.6×（13.1-1-2.1）
=15.6×10
=156
6.4×0.25＋3.6÷4
=6.4×1/4+3.6×1/4
=1/4×（6.4+3.6）
=1/4×10
=5/2