A combination lock on a suitcase has 4 wheels each labeled with digits 1 to 8 How many 4 digit combination lock codes are possible if no digit can be repeated?

the first wheel has 8 possibilities. the second wheel has only 7 possibilities as it cannot be the same as the first. the third wheel has 6 possibilities and the last has only 5 possibilities. 8*7*6*5=1680