Difference between revisions of "2007 Alabama ARML TST Problems/Problem 5"
| Line 7: | Line 7: | ||
==See also== | ==See also== | ||
{{ARML box|year=2007|state=Alabama|num-b=4|num-a=6}} | {{ARML box|year=2007|state=Alabama|num-b=4|num-a=6}} | ||
| + | |||
| + | [[Category:Introductory Combinatorics Problems]] | ||
Revision as of 09:11, 18 June 2008
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
| 2007 Alabama ARML TST (Problems) | ||
| Preceded by: Problem 4 |
Followed by: Problem 6 | |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 | ||
