Respuesta :
slot method
5 slots
1st slot: 9 options
2nd slot:8 options (1 went to first slot)
3rd slot:7
4th:6
5th:5
now multiply them
9*8*7*6*5=15,120 ways
5 slots
1st slot: 9 options
2nd slot:8 options (1 went to first slot)
3rd slot:7
4th:6
5th:5
now multiply them
9*8*7*6*5=15,120 ways