30. In one of the semi-cottage productions, when casting blanks in molds and machining parts from them, only $66 \frac{2}{3} \%$ of the material from each blank was used for each part, and the rest went to chips. To save on the scarce material, the chips were remelted and cast into blanks again. What is the maximum number of parts that can be obtained from 20 identical blanks, and what will be the waste in this case?
30. Having obtained 20 parts from 20 blanks, one-third of the total material will end up as swarf, i.e., the equivalent of $6 \frac{2}{3}$ blanks $\left(20: 3=6 \frac{2}{3}\right)$. From this material, 6 blanks are obtained, and there is still material left for $\frac{2}{3}$ of a blank. Manufacturing 6 parts from this material results in swarf equivalent to $6: 3=2$ blanks. Using this material, 2 blanks are obtained, and 2 parts are machined from them, leaving swarf equivalent to $2: 3=\frac{2}{3}$ of a blank. Thus, in total, there is material for $\frac{2}{3}+\frac{2}{3}=\frac{4}{3}$ blanks. Using this material, one more blank is obtained, from which one part is machined. As a result, 29 parts are obtained, and there is swarf equivalent to $\frac{1}{3}+\frac{1}{3}=\frac{2}{3}$ of a blank.