A certain number ends with the digit 2. Moving the 2 from the end of the number to its front doubles it. Can you find this number?

(Hint: it's quite large)

The tricky part is in the carrying. Initially it's a little awkward, but finally works. Anyways, in your solution you end with 110526315789473684, which of course is wrong. It should be 210526315789473684. The other thing is that you can probably work the problem from left to right, but that would be a huge pain. For example, you know that the first digit has to be a 1 in order to double to a 2. So, the digit next to the 1 has to be 4 or smaller (it can't carry over to the left when doubled). Doing this is an awful pain. Initially I found the number was 105...842, figuring out the middle stuff was what forces you to adopt an algorithm rather than mess around until you get something!

Posted by FingLao on 2002-05-09 09:43:32