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问题: 分数的简便算法

1/1×4+1/4×7+1/7×10+1/10×13+1/13×16

解答:

1/1×4+1/4×7+1/7×10+1/10×13+1/13×16=
1/3[(1/1-1/4)+(1/4-1/7)+(1/7-1/10)+(1/10-1/13)+(1/13-1/16)]
=1/3[1-1/16]
=(1/3)*(15/16)
=5/16