\[\boxed{\mathbf{9.}}\]
\[\textbf{а)}\ 1\ дм = 10\ см\]
\[2\ дм = 20\ см\]
\[5\ дм = 50\ см\]
\[7\ дм = 70\ см\]
\[10\ дм = 100\ см\]
\[\textbf{б)}\ 10\ см = 1\ дм\]
\[30\ см = 3\ дм\]
\[60\ см = 6\ дм\]
\[80\ см = 8\ дм\]
\[100\ см = 10\ дм\]