how many
if you can repeat the numbers then it is combiniations go to AAAA
if you cannot repeat an use only each number once, then go to BBBBB (permutations)
AAAAAA
combinations
4 slots
9^4 is answer isnc you can repeat is answer
9^4=6561 different ones
BBBBBBB
permutations
slot method
4 slots
9 in 1st
8 in second (1 in first slot
7 in 3rd
6 in 4th
9*8*7*6=3024 ways
if you can repeat numersals then answer is 6561 ways (combinations)
if you cannot repeat then answer is 3024 ways (permutations)
