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
_____________________________________________

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

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/