2007 Alabama ARML TST Problems/Problem 5

Revision as of 09:10, 18 June 2008 by 1=2 (talk | contribs) (New page: ==Problem== How many positive 5-digit odd integers are palindromes? ==Solution== The units digit must be odd, and the ten-thousands digit must be equal to the units digit. So there are 5 ...)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

Problem

How many positive 5-digit odd integers are palindromes?

Solution

The units digit must be odd, and the ten-thousands digit must be equal to the units digit. So there are 5 possible choices there. Then there are ten choices for the tens and hundreds digits, but the thousands digit is fixed. Therefore there are 5*20*20=500 5-digit odd palindromes.

See also