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问题: 计算题

计算: 1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/80

解答:

1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/80
=1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/80
=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/80
=1/2 -1/9 +1/80
=7/18 +1/80
=289/720