6.6×4/7+66×1/70+0.66×20/7
=6.6×4/7+(6.6×10)×1/70+0.66×(10×2/7)
=6.6×4/7+6.6×(10×1/70)+(0.66×10)×2/7
=6.6×4/7+6.6×1/7+6.6×2/7
=6.6×(4/7+1/7+2/7)
=6.6×1
=6.6
6.6×4/7＋66×1/70＋0.66×20/7
1/70(6.6×40＋66＋0.66×200)
1/70×6.6×（40+10+20）
6.6×1/70×70
6.6
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