Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Missing digit

  1. Dec 3, 2004 #1

    BobG

    User Avatar
    Science Advisor
    Homework Helper

    I have a five digit number - no, it's not that easy
    I rearrange the digits and subtract the smaller number from the larger.

    The difference is also a five digit number. I jumble up the digits of the difference. Four of the digits of the difference are 2172.

    What's the missing digit of the difference?
     
    Last edited: Dec 3, 2004
  2. jcsd
  3. Dec 4, 2004 #2
    brute force , hapahazard hand waving and abra cadabras are giving me the missing digit as ::6::

    Let me see if i can see through some technique here ....
    interesting problem btw.

    -- AI
     
  4. Dec 4, 2004 #3

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    The missing digit would have to be 6 since the difference must be a multiple of 9.
     
  5. Dec 4, 2004 #4
    duh! ofcourse!

    -- AI
    **i should sincerely stop playing notpron, i am losing sight of the obvious**
     
  6. Dec 5, 2004 #5
    i'm missing something, why does it have to be a multiple of 9?
     
  7. Dec 5, 2004 #6
    Remember (10^k - 1) is always multiple of 9.
    So, for each digit A , you have:
    A*10^n - A*10^m = A*(10^n - 10^m) which is multiple of 9 .
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...
Similar Threads for Missing digit Date
Future of Analog in Amateur Radio Jan 24, 2017
News EgyptAir Flight Missing May 19, 2016
News Any of you guys missing an airplane (or three)? Dec 8, 2015
Some seat numbers missing on flight Dec 7, 2015
Miss my childhood Aug 23, 2014