1/2+1/6+1/12+1/20+1/30;1/2×3+1/3×4+1/4×5+1/5×6+1/6x7

1/2+1/6+1/12+1/20+1/30;1/2×3+1/3×4+1/4×5+1/5×6+1/6x7
1/2+1/6+1/12+1/20+1/30;1/2×3+1/3×4+1/4×5+1/5×6+1/6x7

1/2+1/6+1/12+1/20+1/30;1/2×3+1/3×4+1/4×5+1/5×6+1/6x7

拆分开来算

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第二问等于7

5/6

1/2+1/6+1/12+1/20+1/30=1/2+1/2x3+1/3×4＋1/4×5＋1/5×6=1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=5/6

5/6