
展开全部
1.9+2.9+3.9+4.9+5.9
=(2-0.1)+(3-0.1)+(4-0.1)+(5-0.1)+(6-0.1)
=(2+3+4+5+6)-(0.1+0.1+0.1+0.1+0.1)
=20-0.5
=19.5
=(2-0.1)+(3-0.1)+(4-0.1)+(5-0.1)+(6-0.1)
=(2+3+4+5+6)-(0.1+0.1+0.1+0.1+0.1)
=20-0.5
=19.5
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