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 Find just one digit (Posted on 2005-11-10)
If ABC+DEF+GHI=JJJ, each letter stands for a different digit, and no number starts with zero, what is J?

 See The Solution Submitted by Federico Kereki Rating: 3.8000 (5 votes)

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 Puzzle Solution Comment 13 of 13 |

ABC+DEF+GHI=JJJ
-> ABC+DEF+GHI+10J =JJJ + 10J = 111J+10J = 121J
-> ABC+DEF+GHI+J =4J(mod (9).....(#)

Now, the letters A to J (in order) taken together corresponds to a permutation of the digits 0 to 9 (in order), and accordingly:
ABC+DEF+GHI+J = A+b+C+D+E+F+G+H+I+J(mod 9)
= 0+1+2+3+4=5+6+7+8+9 (mod 9)
= 45 (mod 9)
= 0 (mod 9)

Accordingly, from (#), we must have:

4J = 0(mod 9)

Since gcd(4,9) = 1, it folows that:

J = 0(mod 9)

Thus J is a decimal digit which is divisible by 9. Accordingly, J = 0, or 9. Since, none of the numbers can contain any leading zero, we observe that J=0 leads to a contradiction. Therefore, J=9.

It now remains to verify that there is at least one valid solution to the given problem. By means of trial and error, we observe that indeed there are many valid solutions to the given problem. four of the said solutions are as follows:

567+328+104= 999
258+637+104= 999
368+527+104=999
237+658+104=999

Consequently, the required value of J is 9.

 Posted by K Sengupta on 2009-01-28 11:43:42

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