Given the set of digits{2,3,4,7,8,9} how many three-digit numbers can be formed?

Hope there is a magic Formula, that someone knows, otherwise:
You could start with 234, 237, 238, 239. 243, 247, 248, 249, 273, 274,278, 279, 283, 284, 287, 289, 293, 294, 297, and 298.
See if I missed some of the set that starts with a 2. I would think ever how many numbers is found with 2's should be able to be multiplied by 6, as each number should have the same to a starting number.
Couple of good Math Guys/Girls? Could give good input.

If repetition is allowed, then there are

numbers that can be formed.

If repetition is not allowed, then there are

numbers that can be formed.

When forming 3 digit numbers, order is important.

So,

Stratmando, you're on the right track. You have 20 listed that start with 2.

There are 6 digits, so 20*6=120

Galactus, I was going to mention you, but didn't wan't to leave someone out so I mentioned no one
Hey, Cool that it works out(20 combinations X 6 = 120).
I love Math and figuring, barely made it through High School. I Love solving problems.

Galactus,
I have a couple of Locks, I lost the Keys, and when pulling the pins, I accidentally dumped them, there are 4 different pins, 2 are the same length, What are the total number of keys to be made to insure 1 of them works?

Thanks, you are ALWAYS good on this stuff. Take care.

Given the set of digits{2,3,4,7,8,9} how many three-digit odd numbers can be formed

Half as many as in your previous question.