counting question

534  543  634  643  734  743  834  843  934  943  Total =  10 such numbers

Actually, guest, though you are right, there is a way to solve this without seperatly finding each and every one of the numbers. We can use counting ;)

no, counting is not the type of counting you learned in preschool, it's premutations, the kind you use for combonations. 

We can think of the number as 3 giant spaces:

–––––     ––––––    ––––––

The number in those amount of spaces is the possible numbers for the input:

    5              2              1

–––––     ––––––    ––––––

Now, all we have to do is multiply them all out:

5 * 2 * 1 = 10 possible numbers

And guest, you are correct. The 10 possible numbers are:

534  634  734  834  934   

543  643  743  843  943

:)