how many unique 10 digit numbers can be formed if the number 2 is in the first place and repetition is allowed?
+680 10 digit numbers go something like this: _ _ _ _ _ _ _ _ _ _
If number 2 is in the first place, it's kind of set so you basically only need to find 9 digit numbers now: _ _ _ _ _ _ _ _ _
If repition is not allowed, the first digit has 9 (no 0) choices the second also has 9 (because any number except the first chosen) the third has 8, and so on. That's basically going to be 9*9! (without the 1 but anything times 1 does nothing)
Try figuring that out!
