A password for an online contest must be a five-digit positive integer (thus its…
MATHEMATICS · Multi-part · AoPS · Mathematics · Follow the Rules · Follow the Rules
Problem
A password for an online contest must be a five-digit positive integer (thus its first digit cannot be 0).
(i) How many five-digit positive integers are possible in total?
(ii) How many such passwords are possible if no two consecutive digits in the number are identical?