1. The problem statement, all variables and given/known data How can you convert 212 in base-10 to base-9? 3. The attempt at a solution There are holes in the sequence of figures when considering 212 in base-9. There are 21 holes in the line. There also holes from 90 to 99 and from 190 to 199. There are then 40 (= 23+10+10-1) holes in the line, since 198 belongs to the previous sets already. This suggests me that the figure in base-9 is at least 242. However, the correct answer is 248.