3 ms·
I guess the trick is there aren't that many possibilities, so you precomputed them all can search through the list.
by Raphael 17y ago
I guess the trick is there aren't that many possibilities, so you precomputed them all can search through the list.
- RiderOfGiraffes 17y agoYou can choose any collection of digits and multiply them together. Then you can choose any digit of the answer as your secret, and you can list the remaining digits in any order you like. Trust me, there are lots of possibilities. No, that's not the trick.
- fh 17y agoI'm sure there's a cute mathematical trick to calculate the missing digit, but Raphael is right, with numbers limited to 1 billion, this can be easily brute forced. You need a few gigabytes of disk space and a few days of precalculation at most. What's more interesting to me is that the missing number is actually unique, i.e. that this trick is possible at all. Maybe it actually isn't, maybe it doesn't work in 0.1% of the cases, which is good enough for a magic trick.
- RiderOfGiraffes 17y agoIt works in very nearly (but not quite) 95% of cases.
- RiderOfGiraffes 17y agoI should also have said - this trick doesn't rely on the limit of the number of digits, it works with any number of digits. Use an arbitrary precision package or sensible language, multiply numbers together for as long as you like, then tell me all but one of the digits in the answer, and 95% of the time I can tell you the one you left out.
- RiderOfGiraffes 17y agoPerhaps. But I can do this live, without assistance.