1. Answer: 24
Explanation:
There are 4 cities to choose from. After visiting the 1st city, there are only 3 cities to choose from, etc (see below).
1st city and 2nd city and 3rd city and 4th city
4 x 3 x 2 x 1 = 24
2. Answer: 30,240
Explanation:
There are 10 digits to choose from. After choosing the first digit, there are only 9 digits to choose from (because you can't have duplicate digits in the combination) (see below).
1st digit and 2nd digit and 3rd digit and 4th digit and 5th digit
10 x 9 x 8 x 7 x 6 = 30,240