Phone Number CombinationsDate: 05/07/2000 at 13:54:09 From: Sonja Moussa Subject: Probability Linda knows the first 3 digits of Jack's phone number, which are 297, but she doesn't know the other 4. All she remembers is that the rest of the digits are 2's, 9's and 7's. What is the maximum number of times that Linda (who is very unlucky) will have to try until she gets the right number? Date: 05/08/2000 at 15:10:03 From: Doctor Anthony Subject: Re: Probability You can model this as the number of different ways you could put 4 balls at random into 3 cells (numbered 2, 9 and 7) such that no cell is empty. The answer is 36 in this case. It is the value T(4,3). For an explanation of the function T(n,m), see: Collecting a Set of Coupons http://mathforum.org/dr.math/problems/amal2.2.3.00.html There, I have also given a general description of the method that allows you to calculate far more difficult problems. - Doctor Anthony, The Math Forum http://mathforum.org/dr.math/ |
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