For a privately developed group housing project, the ratio of total number of dwelling units of HIG : MIG : LIG is 3:2:1. The proposed average size of HIG, MIG and LIG units in sq.m are 100, 60 and 30 respectively. The ratio of the total built up area between (MIG + LIG) to HIG will be 1: \underline{\hspace{1cm}} [in integer].