Question

一乘二分之一加二乘三分之一加...加五十乘五十一分之一 等于几?

Answer 1

1/(1*2)+1/(2*3)+1/(3*4)+.+1/(50*51)
=1-1/2+1/3-1/4+.+1/50-1/51
=1-1/51
=50/51
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