Channel: Vsauce2

Category: Education

Tags: math shortmind blowingmath riddlesbrain teasers mathbrain teaser puzzlesvsaucemath tricksurviving the deadliest gamerandom gamesvsauce2 birthday paradoxgame you quitbrain teasers for kidsvsauce2math puzzlemath magicvsauce2 gamevsausewhat is a paradoxmath gamesant on a rubber rope vsaucemath puzzles for kidsmath caught a serial killervsause2game theorybrain teasersmath paradoxvsauce2 paradoxprobability games

Description: You can take any number with 2 or more digits and determine almost instantly whether it's divisible by 11, and the method is actually really, really easy -- even for a number like 2,399,317,565,387,204. All it takes is simple addition and alternating between the odd and even digits. If the difference between the two sums is 0 or a number that's divisible by 11, then the entire number is divisible by 11. It's that easy. Think about it with a 2-digit number like 33. The difference between the first digit (3) and the second digit (3) is 0, and 33 is obviously divisible by 11. 121? (1 + 1) = 2, and the even digit is also 2 -- 121 is divisible by 11. Try this with a number that has... 137 digits. GO. #shorts