Question 1122813
{{{ (1/2)*n*( n+1 ) = 1225 }}}
{{{ n*( n+1) = 2450 }}}
{{{ n^2 + n - 2450 = 0 }}}
{{{ ( n - 49 )*( n + 50 ) = 0 }}}
{{{ n = 49 }}}
1225 is the sum from 1 to 49
( I actually checked this on my calculator )