1.

1 + \frac { 1 } { ( 1 + 2 ) } + \frac { 1 } { ( 1 + 2 + 3 ) } + \ldots + \frac { 1 } { ( 1 + 2 + 3 + \ldots n ) } = \frac { 2 n } { ( n + 1 ) }

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