Akey code must contain 4 numerals. there are 9 numerals available . using these numerals, how many different key codes may be created ?

How many
if you can repeat the numbers then it is combiniations go to
if you cannot repeat an use only each number once, then go to (permutations)


combinations
4 slots
9^4 is answer isnc you can repeat is answer
9^4=6561 different ones


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)