Answer:
2.4
Step-by-step explanation:
Answer:
b
Step-by-step explanation:
The number of permutations of the 25 letters taken 2 at a time (with repetitions) is:

The number of permutations of the 9 digits taken 4 at a time (with repetitions) is:

Each permutation of letters can be taken with each permutation of digits, therefore the total number of possible passwords is:
Answer:
90
Step-by-step explanation:
100%-10%=90%
90%->81
10%->9
100%->9+81=90