27:4 mal ? = 1638

27/4 * x = 1638                      x = 1638 / (27/4)  = 1638*4 /27

6,75 *x = 1638           

         x = 1638 / 6,75 = 242,6666...

$${\frac{{\mathtt{1\,638}}{\mathtt{\,\times\,}}{\mathtt{4}}}{{\mathtt{27}}}} = {\frac{{\mathtt{728}}}{{\mathtt{3}}}} = {\mathtt{242.666\: \!666\: \!666\: \!666\: \!666\: \!7}}$$

Gruß radix !