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Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

729.0. "census taker" by VINO::JMUNZER () Wed Jul 08 1987 12:38

This is very closely related to a couple of earlier notes.  HANDS OFF if
you know the general idea.

John

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Census taker:  "How many people live here, and what are their ages?"

Resident:  "Three people live here.  The product of our ages is 225."

Census taker:  "What are the ages?"

Resident:  "The sum of our ages is the house number."

Census taker:  "What are the ages?"

Resident:  "I'm the eldest, and I've told you all you need to know about
the other two."

Census taker:  "Okay.  Bye."

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What are the ages?
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729.1IJSAPL::PTTCS_TONYFri Jul 10 1987 07:5310
    


    I imagine that there is some significance in the statement relating
    to the sum of the ages but it eludes me entirely!
    
    A fairly simple numerical task yeilds 4 possible answers to this
    problem, but again, I think I'm maybe missing the WHOLE point.
    
    
729.2IJSAPL::PTTCS_TONYFri Jul 10 1987 08:0511
    

    Should have added : -
    
    Each of the four possible solutions yield unique values on summation
    of the three integers, so knowing the house number would provide
    the questioner with a single, correct solution...BUT
    
    There has got to be a more elegant method of solving this problem!!!
    
     
729.3Clarification?SQM::HALLYBLike a breath of fresh water...Fri Jul 10 1987 10:347
    "Eldest" implies strictly greater than, right?  (I mean, you could
    have three 7-year-olds and one could still be "eldest...)
    
    Ages and house numbers are positive integers, right?  (E.g., you
    don't wish to admit ages of 10, 7�, and 3 and an address of 20�).
    
      John
729.4CLT::GILBERTeager like a childFri Jul 10 1987 12:205
    Yes, assume that the ages are all positive integers less than 200,
    that "eldest" implies a unique greatest integer age, the house number 
    is a positive integer, the census taker knows the house number, and
    needs to know the ages, and that the census taker and resident tell
    no lies.
729.5"I am the cleverest????"KEEPER::DEHOLLANFri Jul 10 1987 19:086
    Re .4
    Your "clarification" sure messed up my dimwit solution:
    Take "I am the eldest" in the same sense as when Muhammed Ali
    says "I am the greatest," then the house number stuff is just
    hokum and the resident talking is 225 years old, the other two
    are 1 each.
729.6SSDEVO::LARYFri Jul 10 1987 21:474
Another assumption which helps is that the census taker is very smart -
i.e. the census taker did not ask about ages the third time because he/she
was dim.....

729.7I think I got itBANDIT::MARSHALLhunting the snarkMon Jul 13 1987 17:4828
    here tis...
    
    the factors of 225 are 5,5,3,3,1; all combinations below:
    
    	A	B	C        SUM
       ---     ---     ---       ---
       5*5      3       3         31
       5*3      5       3         23
       3*3      5       5         19
      5*5*3     3       1         79
      5*3*3     5       1         51
       5*5     3*3      1         32
       5*3     5*3      1         31
     5*5*3*3    1       1        227                         
    
    knowing the house number still left the census taker confused, so
    the correct combination must be one of the two that sum to 31.
    knowing that A is the eldest (and not a twin) yields the unique
    solution of:
    
    25, 3, 3
       
                                                   
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729.8solvedVINO::JMUNZERTue Jul 14 1987 09:133
    .7 is right.
    
    John