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Palindromic Numbers


Date: 08/30/97 at 00:50:08
From: windows
Subject: Palindromic numbers

How many palindromic numbers are there between 

   a) 10-100
   b) 100-1000
   c) 10-100000   ?

Date: 09/03/97 at 10:47:03
From: Doctor Rob
Subject: Re: Palindromic numbers

a) Two-digit palindromes must have identical digits.  You have 
   9 choices for the first digit (0 is excluded), and the second 
   digit is determined for each, so the answer is 9.

b) Three-digit palindromes must have identical first and last 
   digits, but the middle digit is a free choice.  There are 
   9 choices for the first digit (0 is excluded), and for each  
   choice, there are 10 choices for the middle digit, so the 
   answer is 9*10.

c) 9 + 9*10 + 9*10 + 9*10^2 = 1089.  Can you explain why?

-Doctor Rob,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/

Associated Topics:
Elementary Number Sense/About Numbers
Middle School Number Sense/About Numbers

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