Question

6分之1+12分之1+20分之1+30分之1+42分之1+90分之1=

Answer 1

6分之1+12分之1+20分之1+30分之1+42分之1+90分之1

=1/(2×3)+1/(3×4)+1/(4×5)+1/(5×6)+1/(6×7)+1/(9×10)

=1/2-1/3+1/3-1/4+.+1/6-1/7+1/9-1/10

=1/2-1/7+1/9-1/10

=5/14+1/90

=116/315;

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