cong tac tif vung nay den vung khac roi sinh cd lapT r a lofi:Ngiidi Viet quan niem n h i i n g so' 3, 5, 7 la nhflng so'le thuoc ve so' difdng, so' c h i n la so' am. NgUdi ci ndidifdng the sii dung so' dUdng. Chang han: xay nha t h ixay 3 gian, 5 gian, xay bac t h i tam cap (3 bac), th&phU[r]