[tex]Let's\ convert\ decimeter\ to\ centimeter... \\ \\ 3dm\ \cdot \frac{10cm}{1dm}\to3\times10cm\to\boxed{30cm.} \\ \\ We\ have\ now\ the\ complete\ set\ where\ 3dm=30cm. \\ \\ Solution; \\ \\ 12cm:30cm\to \frac{12}{6}: \frac{30}{6}\to\boxed{\boxed{2:5}} \\ \\ Hope\ it\ Helps:) \\ Domini [/tex]
