1. How many words of length w can be made using an alphabet with l letters?
2. How many telephone numbers have no 0 in the prefix (the first three numbers before the hyphen)?
3. True or false: if A∩B∩C = 0, then the sum principle applies so / |A∪B∪C|= |A|+|B|+|C|.
4. How many words of length w can be made using a set of alphabets with aj letters for the jth letter in a word?