Combinations are NOT all exponential. The very first problem he was given illustrates that. It is a straight up permutation problem, which is factorial.combinations are all exponential. A password is the same as a combination lock with wheels. How many digits on each wheel, how many wheels.

Example: 3 wheels, each with 0-9. that's 10 digits on 3 wheels. combinations: 10^3

Example: 5 wheels, 26 digits: 26^5