\[\eqalign{& \,\,\,\,\,\,\,\,2dm\,\,\,\, = \,\,\,20\,\,\,cm\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,20cm\,\,\,\, = \,\,\,2\,\,dm \cr& \,\,\,\,\,\,\,\,3dm\,\,\,\, = \,\,\,30\,\,cm\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,30cm\,\,\,\, = \,\,\,3\,\,\,dm \cr& \,\,\,\,\,\,\,\,5dm\,\,\,\, = \,\,\,50\,\,\,cm\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,50cm\,\,\,\, = \,\,5\,\,\,dm \cr& \,\,\,\,\,\,\,9dm\,\,\,\, = \,\,\,90\,\,cm\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,90cm\,\,\,\, = \,\,\,9\,\,\,dm \cr} \]
1. a] Số?
\[1dm\,\,\, = \,\,\,\,cm\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,10cm\,\,\, = \,\,\,\,dm\]
b] Viết 1dm, 2dm vào chỗ chấm thích hợp:
2. Số?
3. Điền dấu >, \,\,\,\,40cm\, \cr
& 3dm\,\,\,\, > \,\,\,20cm\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,1dm\,\,\,\, + \,\,\,4dm\,\,\, < \,\,\,\,60cm\, \cr} \]
4.