1.

If sum _(r=1)^(n) t_(r) = (1)/( 12) n (n+1) (n+2) then sum_(r=1)^(n)(1)/( t_r)

Answer»

`(2N)/( n+1)`
`(4N)/( n+1)`
`(3N)/( n+2)`
`(3n)/( n+1)`

ANSWER :B


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