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* * * OFF TOPIC * * * Permutations of matching 7 out of 9 numbers

Posted By: Bob Koca
Date: Friday, 18 March 2016, at 5:52 p.m.

In Response To: * * * OFF TOPIC * * * Permutations of matching 7 out of 9 numbers (Jake Jacobs)

I will ignore the group of zeros restrictions since it will barely matter, will make the calculation depend on the initial number, and I don't feel like doing it right now.

To get a 7 of 9 match there are 9C7 = 36 ways to choose which positions will be matched. Those positions have 1 choice of digit and the other two will have 9 choices of digit (must be different because said wanted exactly 7 matches). This gives 36 x 9 x 9 = 2916 such numbers.

If one has a starting SSN and another is chosen randomly there is about a 1 in 343,000 chance of getting such a match.

Messages In This Thread

• * * * OFF TOPIC * * * Permutations of matching 7 out of 9 numbers
  leobueno -- Wednesday, 16 March 2016, at 10:07 p.m.
  • * * * OFF TOPIC * * * Permutations of matching 7 out of 9 numbers
    Bob Koca -- Thursday, 17 March 2016, at 3:02 a.m.
    • * * * OFF TOPIC * * * Permutations of matching 7 out of 9 numbers
      Jake Jacobs -- Friday, 18 March 2016, at 2:24 a.m.
      • * * * OFF TOPIC * * * Permutations of matching 7 out of 9 numbers
        Bob Koca -- Friday, 18 March 2016, at 5:52 p.m.
      • * * * OFF TOPIC * * * Permutations of matching 7 out of 9 numbers
        leobueno -- Monday, 21 March 2016, at 2:01 a.m.