Drexel dragonThe Math ForumDonate to the Math Forum

Ask Dr. Math - Questions and Answers from our Archives
_____________________________________________
Associated Topics || Dr. Math Home || Search Dr. Math
_____________________________________________

Phone Number Combinations


Date: 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/   
    
Associated Topics:
College Probability
High School Probability

Search the Dr. Math Library:


Find items containing (put spaces between keywords):
 
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

_____________________________________
Math Forum Home || Math Library || Quick Reference || Math Forum Search
_____________________________________

Ask Dr. MathTM
© 1994-2013 The Math Forum
http://mathforum.org/dr.math/