$\begin{array}{l}36\times a\times b\times c\times d=\overline{4449m00}\\\Leftrightarrow 4\times9\times a \times b\times c\times d=\overline{4449m00}\\\Rightarrow \overline{4449m00} \,\,\vdots\,\,4;9 \\\text{- Số }\overline{4449m00}\,\,\vdots\,\,4\\\Leftrightarrow 00 \,\,\vdots\,\, 4\text{ (luôn đúng)}\\\Rightarrow \overline{4449m00}\,\,\vdots\,\,4\\\text{- Số }\overline{4449m00}\,\,\vdots\,\,9\\\Leftrightarrow 4+4+4+9+m+0+0\,\,\vdots\,\,9\\\Leftrightarrow 21+m\,\,\vdots\,\,9\\\text{mà $m$ là chữ số}\\\Rightarrow \text{Để $21+m\,\,\vdots\,\,9$ thì $m=6$}\\\text{- Vậy $m=6$}\end{array}$
